Creating/Solving One Variable Equations/Inequalities
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Algebra 2 › Creating/Solving One Variable Equations/Inequalities
A medication dose starts at 200 mg. Each hour, 15% of the medication is eliminated (so 85% remains). Model the amount remaining after $t$ hours with an exponential equation and solve for when 50 mg remains.
Let $t$ = time in hours.
Model: $200-0.15t=50$. Then $t=1000$ hours. It takes 1000 hours.
Model: $200(0.85)^t=50$. Then $t=\log_{0.85}(0.25)\approx 8.54$ hours. It takes about 8.54 hours for 50 mg to remain.
Model: $200(1.15)^t=50$. Then $t=\log_{1.15}(0.25)\approx -10.00$ hours. It takes about -10 hours.
Model: $200(0.15)^t=50$. Then $t=\log_{0.15}(0.25)\approx 0.69$ hours. It takes about 0.69 hours.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Exponential growth/decay problems arise when something grows or shrinks by a constant percent: 'eliminates 15% hourly' means 85% remains, so multiply by 0.85 each hour, giving formula amount = initial × $(0.85)^t$. To find when it reaches a specific value, set up equation like $200(0.85)^t$ = 50 and solve using logarithms: $(0.85)^t$ = 50/200 = 0.25, so t = ln(0.25)/ln(0.85) ≈ 8.54 hours. The logarithm unlocks the exponent! Since 15% is eliminated each hour, 85% remains, so the medication amount after t hours is $200(0.85)^t$ mg, and we solve $200(0.85)^t$ = 50 by dividing both sides by 200 to get $(0.85)^t$ = 0.25, then taking logarithms: t = log₀.₈₅(0.25) ≈ 8.54 hours. Choice C correctly models exponential decay as $200(0.85)^t$ (since 85% remains each hour) and solves using logarithms to find t ≈ 8.54 hours. Choice A incorrectly uses 0.15 as the base (which would mean only 15% remains each hour), B uses 1.15 which would represent 15% growth not decay, and D treats it as linear decay subtracting 0.15t instead of multiplying by $(0.85)^t$. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A tank is being filled by two hoses. Hose A can fill the tank in 6 hours and Hose B can fill the same tank in 9 hours.
Write and solve an equation to find how long it takes to fill the tank if both hoses run together.
Let $t$ = the number of hours to fill the tank together.
Set up $6+9=t$. Then $t=15$ hours. The tank fills in 15 hours.
Set up $\frac{1}{6}-\frac{1}{9}=\frac{1}{t}$. Then $t=18$ hours. The tank fills in 18 hours.
Set up $\frac{1}{6}+\frac{1}{9}=\frac{1}{t}$. Then $t=\frac{18}{5}$ hours. The tank fills in $3.6$ hours.
Set up $\frac{1}{6}+\frac{1}{9}=t$. Then $t=\frac{5}{18}$ hours. The tank fills in about $0.28$ hours.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Work-rate problems lead to rational equations: if one worker completes a job in time t₁ and another in t₂, their combined rate is 1/t₁ + 1/t₂ (adding rates), which equals 1/t_combined. The reciprocals represent 'fraction of job per hour,' and adding these fractions gives the combined rate. Solving these rational equations requires finding LCD and often produces fractional time answers that make sense: 3.4 hours = 3 hours 24 minutes. For this tank-filling scenario, set up the equation as 1/6 + 1/9 = 1/t; finding a common denominator of 18 gives (3 + 2)/18 = 5/18, so 1/t = 5/18 and t = 18/5 = 3.6 hours, meaning together they fill the tank in 3 hours and 36 minutes. Choice A correctly sets up the equation by adding the rates and solves to find t = 18/5 hours, which is the accurate combined time. A common distractor like choice B forgets to take the reciprocal after adding the rates, leading to an unrealistically small time that doesn't make sense for combined effort. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A community pool has two pumps that can fill it. Pump A can fill the pool in 6 hours, and Pump B can fill the pool in 8 hours.
Write and solve a rational equation to find how long it takes to fill the pool if both pumps run at the same time.
Let $t$ = the time (in hours) to fill the pool together.
Set up $\frac{1}{6}+\frac{1}{8}=\frac{1}{t}$. Then $t=\frac{14}{3}$ hours, so it takes about 4.67 hours together.
Set up $\frac{1}{6}+\frac{1}{8}=\frac{1}{t}$. Then $t=\frac{24}{7}$ hours, so it takes about 3.43 hours together.
Set up $\frac{6}{t}+\frac{8}{t}=1$. Then $t=14$ hours, so it takes 14 hours together.
Set up $6+8=t$. Then $t=14$ hours, so it takes 14 hours together.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Work-rate problems lead to rational equations: if one worker completes a job in time t₁ and another in t₂, their combined rate is 1/t₁ + 1/t₂ (adding rates), which equals 1/t_combined. The reciprocals represent 'fraction of job per hour,' and adding these fractions gives the combined rate. Solving these rational equations requires finding LCD and often produces fractional time answers that make sense: 3.4 hours = 3 hours 24 minutes. For this pool-filling scenario, set up the equation as 1/6 + 1/8 = 1/t; find a common denominator of 24 to get 4/24 + 3/24 = 7/24 = 1/t, so t = 24/7 ≈ 3.43 hours, meaning both pumps together fill the pool in about 3 hours 26 minutes. Choice B correctly sets up the equation by adding the rates and solves to find t = 24/7 hours, accurately determining the combined time. A common mistake, as in choice C, is adding the individual times instead of the rates, which overestimates the combined time since they work together faster. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A ball is thrown upward from a platform. Its height (in feet) after $t$ seconds is modeled by $h(t)=-16t^2+48t+64$. Write and solve an equation to find when the ball hits the ground.
Let $t$ = time in seconds (use the solution that makes sense in context).
Set $-16t^2+48t+64=0$. Solution: $t=2$. The ball hits the ground at $t=2$ seconds.
Set $-16t^2+48t+64=0$. Solutions: $t=4$ and $t=-1$. The ball hits the ground at $t=4$ seconds.
Set $-16t^2+48t+64=0$. Solutions: $t=4$ and $t=1$. The ball hits the ground at $t=1$ second.
Set $-16t^2+48t+64=0$. Solutions: $t=1$ and $t=-4$. The ball hits the ground at $t=1$ second.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Projectile motion problems lead to quadratic equations: the height function h(t) = -16t² + v₀t + h₀ represents vertical motion under gravity, where -16 is half the acceleration due to gravity (in ft/s²), v₀ is initial velocity, and h₀ is initial height. The ball hits the ground when h(t) = 0. Setting -16t² + 48t + 64 = 0 and dividing by -16: t² - 3t - 4 = 0. Factoring: (t-4)(t+1) = 0, giving t = 4 or t = -1. Since time cannot be negative in this context, t = 4 seconds. We can verify: h(4) = -16(16) + 48(4) + 64 = -256 + 192 + 64 = 0 ✓. Choice A correctly sets the height equation equal to zero (-16t² + 48t + 64 = 0) and solves to get t = 4 and t = -1, properly rejecting the negative time to conclude the ball hits the ground at t = 4 seconds. Choice B incorrectly states the solutions are t = 1 and t = -4, but substituting t = 1 gives h(1) = -16 + 48 + 64 = 96 feet, not 0. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A number and its reciprocal have a sum of $\frac{10}{3}$.
What equation represents this context? Solve it and interpret the solutions.
Let $x$ = the number (assume $x\ne 0$).
Set up $x-\frac{1}{x}=\frac{10}{3}$. Then $3x^2-10x-3=0$, so $x=3$ or $x=\frac{1}{3}$.
Set up $\frac{1}{x}=\frac{10}{3}x$. Then $x=\pm\sqrt{\frac{3}{10}}$, so the number is $\pm\sqrt{\frac{3}{10}}$.
Set up $x+\frac{1}{x}=\frac{10}{3}$. Then $3x^2-10x+3=0$, so $x=3$ or $x=\frac{1}{3}$.
Set up $x+\frac{1}{x}=\frac{10}{3}$. Then $3x^2-10x+3=0$, so $x=\frac{3}{10}$ only.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Reciprocal relationships often lead to rational equations that become quadratic: for x + 1/x = k, multiply by x to get x² - kx + 1 = 0, solved via quadratic formula, with solutions being reciprocals if valid. For this number, set up x + 1/x = 10/3, multiply by 3x to clear fractions: 3x² + 3 = 10x, rearrange to 3x² - 10x + 3 = 0, factor as (3x - 1)(x - 3) = 0, so x = 3 or x = 1/3, meaning the numbers are 3 and its reciprocal 1/3. Choice A correctly sets up the sum equation and solves to find both solutions x = 3 and x = 1/3. A mistake like in choice C changes addition to subtraction, altering the relationship and solutions. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A number and its reciprocal have a sum of $\frac{10}{3}$.
What equation represents this context? Solve it and interpret the solutions.
Let $x$ = the number (assume $x\ne 0$).
Set up $\frac{1}{x}=\frac{10}{3}x$. Then $x=\pm\sqrt{\frac{3}{10}}$, so the number is $\pm\sqrt{\frac{3}{10}}$.
Set up $x+\frac{1}{x}=\frac{10}{3}$. Then $3x^2-10x+3=0$, so $x=\frac{3}{10}$ only.
Set up $x+\frac{1}{x}=\frac{10}{3}$. Then $3x^2-10x+3=0$, so $x=3$ or $x=\frac{1}{3}$.
Set up $x-\frac{1}{x}=\frac{10}{3}$. Then $3x^2-10x-3=0$, so $x=3$ or $x=\frac{1}{3}$.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Reciprocal relationships often lead to rational equations that become quadratic: for x + 1/x = k, multiply by x to get x² - kx + 1 = 0, solved via quadratic formula, with solutions being reciprocals if valid. For this number, set up x + 1/x = 10/3, multiply by 3x to clear fractions: 3x² + 3 = 10x, rearrange to 3x² - 10x + 3 = 0, factor as (3x - 1)(x - 3) = 0, so x = 3 or x = 1/3, meaning the numbers are 3 and its reciprocal 1/3. Choice A correctly sets up the sum equation and solves to find both solutions x = 3 and x = 1/3. A mistake like in choice C changes addition to subtraction, altering the relationship and solutions. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A community pool is being filled by two hoses. Hose A can fill the pool in 6 hours, and Hose B can fill the pool in 8 hours. If both hoses run at the same time, write and solve a rational equation to find how long it takes to fill the pool.
Let $t$ = the time (in hours) to fill the pool using both hoses together.
Set up $\frac{6+8}{2}=t$. Then $t=7$ hours. The pool fills in 7 hours.
Set up $\frac{1}{6}+\frac{1}{8}=\frac{1}{t}$. Then $t=\frac{24}{7}$ hours $\approx 3.43$ hours. The pool fills in about 3.43 hours.
Set up $\frac{1}{6}-\frac{1}{8}=\frac{1}{t}$. Then $t=24$ hours. The pool fills in 24 hours.
Set up $\frac{1}{6}+\frac{1}{8}=t$. Then $t=\frac{7}{24}$ hour. The pool fills in $\frac{7}{24}$ hour.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Work-rate problems lead to rational equations: if one worker completes a job in time t₁ and another in t₂, their combined rate is 1/t₁ + 1/t₂ (adding rates), which equals 1/t_combined. The reciprocals represent 'fraction of job per hour,' and adding these fractions gives the combined rate. Solving these rational equations requires finding LCD and often produces fractional time answers that make sense: 3.4 hours = 3 hours 24 minutes. Here, Hose A's rate is 1/6 pool per hour and Hose B's is 1/8, so combined 1/6 + 1/8 = (4+3)/24 = 7/24 = 1/t, thus t = 24/7 ≈ 3.43 hours, meaning the pool fills faster together as expected. Choice B correctly sets up the equation by adding rates and solves for t ≈ 3.43 hours, providing the accurate time to fill the pool. A common mistake, like in Choice A, is setting the sum of rates equal to t instead of 1/t, which gives an incorrect small fraction. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A number and its reciprocal have a sum of $\frac{10}{3}$. Write and solve an equation to find the number.
Let $x$ = the number, with $x\ne 0$.
Set up $x+\frac{1}{x}=\frac{10}{3}$. Then $3x^2-10x+3=0$, so $x=3$ or $x=\frac{1}{3}$. Both satisfy the context.
Set up $x-\frac{1}{x}=\frac{10}{3}$. Then $x=3$ only.
Set up $\frac{1}{x}=\frac{10}{3}x$. Then $x=\pm\sqrt{\frac{3}{10}}$.
Set up $x+\frac{1}{x}=\frac{10}{3}$. Then $x=\frac{10}{3}$ only.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Problems involving a number and its reciprocal lead to rational equations: if the number is x, its reciprocal is 1/x, so their sum gives x + 1/x = 10/3. Multiplying through by x: x² + 1 = 10x/3, then 3x² + 3 = 10x, so 3x² - 10x + 3 = 0. Using the quadratic formula or factoring: (3x - 1)(x - 3) = 0, giving x = 1/3 or x = 3, and both are valid since both have reciprocals. Choice A correctly sets up the equation as number + reciprocal = sum (x + 1/x = 10/3) and solves to get x = 3 or x = 1/3, noting both satisfy the context. Choice B uses subtraction instead of addition, C sets up an incorrect equation 1/x = 10x/3, and D claims only x = 10/3 is the solution without solving the quadratic. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A car rental company charges $\$45$ per day plus a one-time fee of $$30$. You have at most $\$300$ to spend. Create an inequality and find the maximum whole number of days you can rent the car.
Let $d$ = number of days.
Inequality: $45d+30\le 300$. Maximum $d=6$ days.
Inequality: $45d+30\le 300$. Maximum $d=7$ days.
Inequality: $45d-30\le 300$. Maximum $d=7$ days.
Inequality: $45d+30\ge 300$. Maximum $d=6$ days.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Budget constraint problems lead to linear inequalities: the total cost is one-time fee plus (daily rate × days), which must stay within budget, giving 30 + 45d ≤ 300. Solving: 45d ≤ 270, so d ≤ 6, meaning you can rent for at most 6 days. Since we need whole days, the maximum is exactly 6 days. Choice A correctly sets up the inequality as total cost ≤ budget (45d + 30 ≤ 300) and solves to get d ≤ 6, so maximum d = 6 days. Choice B has the correct inequality but incorrectly solves to get d = 7, C subtracts the one-time fee instead of adding it, and D uses ≥ instead of ≤ which would mean we want to spend at least $300. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!
A rectangular patio has an area of $96\text{ m}^2$. Its length is 4 meters more than its width.
Set up a quadratic equation and solve to find the patio’s width and length.
Let $w$ = the width in meters.
Set up $w(w+4)=96$. Then $w^2+4w-96=0$, so $w=12$ (reject $-8$). The patio is $12\text{ m}$ by $16\text{ m}$.
Set up $w+(w+4)=96$. Then $2w+4=96$, so $w=46$. The patio is $46\text{ m}$ by $50\text{ m}$.
Set up $w(w-4)=96$. Then $w^2-4w-96=0$, so $w=12$ (reject $-8$). The patio is $12\text{ m}$ by $8\text{ m}$.
Set up $w(w+4)=96$. Then $w^2+4w-96=0$, so $w=8$ (reject $-12$). The patio is $8\text{ m}$ by $12\text{ m}$.
Explanation
This question tests your ability to translate complex real-world situations into mathematical equations (linear, quadratic, rational, or exponential) and solve them to answer practical questions. Area problems with related dimensions often lead to quadratic equations: if length is width plus a constant, set up area = width × (width + constant), resulting in w² + cw - area = 0, solved via factoring or quadratic formula, rejecting negative roots since dimensions are positive. For this patio, set up w(w + 4) = 96, expand to w² + 4w - 96 = 0, use quadratic formula w = [-4 ± √(16 + 384)]/2 = [-4 ± √400]/2 = [-4 ± 20]/2, so w = 8 or w = -12 (reject negative), meaning width 8 m and length 12 m. Choice A correctly sets up the quadratic with length as w + 4 and solves to find the dimensions 8 m by 12 m. A distractor like choice C mistakenly uses a linear equation by adding sides instead of multiplying for area, resulting in impossible dimensions. Context-to-equation type matching: (1) Constant rates and simple relationships → linear, (2) Area, projectile motion, optimization → quadratic, (3) Combined work rates, mixture concentrations, reciprocal relationships → rational, (4) Percent growth/decay over time → exponential. The context language tells you which type: 'per unit' suggests linear, 'area' suggests quadratic, 'together complete' suggests rational (adding reciprocals), 'percent per year' suggests exponential. Identify the type, then use the appropriate solving method! The reality check is essential: after solving, ask: (1) Does the answer satisfy the original equation? (substitute back), (2) Does it make sense in the real world? (no negative quantities, no fractional discrete items), (3) Have I answered what was asked? (find time, not rate; find width, not area). For rational equations, check that denominators aren't zero. For exponential, verify the value is reasonable for the time scale. This three-part check catches most errors and ensures your math answer is also a real-world answer!