All SAT Math Resources
Example Questions
Example Question #17 : How To Find The Solution For A System Of Equations
If (x + y)2 = 15, and x2 + y2 = 27, what is the value of x2y2?
12
–6
–12
144
36
36
First, let's expand (x + y)2 by using the FOIL method.
(x + y)2 = (x + y)(x + y)
According to the FOIL method, we will multiply the first terms of the binomials, then the outer terms, then the inner terms, and then the last terms. We will then add these four products together.
(x + y)(x + y)= x(x) + x(y) + y(x) + y(y) = x2 + 2xy + y2
We are told that (x + y)2 = 15. Let's replace (x + y)2 with x2 + 2xy + y2.
x2 + 2xy + y2 = 15
Rearranging, we can write the equation as follows:
x2 + y2 + 2xy = 15
The second part of the problem tells us that x2 + y2 = 27. Thus, we can replace x2 + y2 with 27.
27 + 2xy = 15
Subtract 27 from both sides.
2xy = –12
Divide by two.
xy = –6
The question asks us for x2y2. According to one of the properties of exponents, (xy)2 = x2y2. Thus, if we square both sides of the equation xy = –6, we will obtain the value of x2y2.
(xy)2 = (–6)2
x2y2 = 36
The answer is 36.
Example Question #18 : How To Find The Solution For A System Of Equations
In triangle ABC, points A and B are located at the points of intersection between the graphs y = 9 – x2 and y = 3 – x, and point C is located at (p,0), where p < 0. What must be the value of p such that the area of triangle ABC is 50?
–21
–13
–5
–9
–17
–17
First, we need to find points A and B, which we are told form the points of intersection between the graphs y = 9 – x2 and y = 3 – x. In order to solve for these two equations, we can set the value of y in the first equation equal to the value of y in the second and then solve for x.
9 – x2 = 3 – x
Add x2 to both sides.
9 = 3 – x + x2
Subtract 9 from both sides. Then rearrange so that the powers of x are in descending order.
-6 – x + x2 = x2 – x – 6 = 0
Factor x2 – x – 6 by thinking of two numbers that multiply to give –6 and add to give –1. Those two numbers are –3 and 2.
x2 – x – 6 = (x – 3)(x + 2) = 0
Set each factor equal to zero and solve.
x – 3 = 0
x = 3
x + 2 = 0
x = –2
Thus, the points of intersection occur where x = –2 and 3. We can find the y values of the points of intersection by substituting –2 and 3 into either equation. Let's use the equation y = 3 – x.
When x = –2, y = 3 – (–2) = 5. One point of intersection is (–2,5).
When x = 3, y = 3 – 3 = 0. The other point of intersection is (3,0).
Let's assume point A is at (–2,5) and that B is at (3,0). We are told that C is located at (p,0), where p < 0. Let's draw triangle ABC with the information we have so far.
In the figure above, the orange line represents the height from side BC to A.
The area of any triangle is (1/2)bh, where b is the length of the base, and h is the length of the height. We will use BC to represent the base, and the orange line to represent the height.
The length of BC will be equal to 3 – p, since both points lie on the x-axis. The length of the orange line is the distance from CB to point A, which is 5. We can now find a formula for the area and set it equal to 50.
Area of ABC = (1/2)(3 – p)(5) = 50
Multiply both sides by 2.
(3 – p)(5) = 100
Divide by 5.
3 – p = 20
Subtract 3 from both sides.
–p = 17
Multiply both sides by –1.
p = –17.
The answer is –17.
Example Question #21 : Systems Of Equations
The sum of the digits in a positive three-digit whole number is equal to 13. When the digits are reversed, the number's value is decreased by 594. If the first digit must be a prime number, then what is the sum of the squares of the three digits?
77
69
54
75
67
75
Since the number has three digits, there must be a digit in the hundreds place, a digit in the tens place, and a digit in the ones place. Let's let h represent the digit in the hundreds place, t represent the digit in the tens place, and let u represent the digit in the ones place. Thus, we can represent our mystery number as follows:
mystery number = 100h + 10t + u
First, we are told that the sum of the digits is 13. Thus, we can write the following equation.
h + t + u = 13
Next, we are told that reversing the digits decreases the value of the original number by 594. We already established that the original number can be represented as 100h + 10t + u. We can then represent the reversed number as 100u + 10t + h. We can now write the following equation:
original number = 594 + reversed number
100h + 10t + u = 594 + 100u + 10t + h
Let's get the h, t, and u terms on the same side. Subtract h from both sides.
99h + 10t + u = 594 + 100u + 10t
Subtract 10t from both sides.
99h + u = 594 + 100u
Subtract 100u from both sides.
99h – 99u = 594
Since 99 and 594 are divisible by 9, we will divide both sides by 9.
11h – 11u = 66
Divide both sides by 11.
h – u = 6
We are told that the first digit, represented by h, must be prime. Let's solve for h in terms of u by adding u to both sides.
h = 6 + u
Since h is a digit, it can't be larger than 9. (The possible values for a digit are 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9.) The only prime numbers less than 9 are 2, 3, 5, and 7. However, if h were 2, 3, or 5, then u would be negative, and we can't have a negative digit. In short, the only value that h can be is 7.
7 = 6 + u
Since h is 7, u must be 1.
If h = 7 and u = 1, we will solve for t by using the first equation h + t + u = 13.
7 + t + 1 = 13
Subtract 8 from both sides.
t = 5
Since h = 7, t = 5, and u = 1, the number must be 751. We are told to find the squares of the digits.
sum of squares of digits = 72 + 52 + 12 = 49 + 25 + 1 = 75.
The answer is 75.
Example Question #22 : Systems Of Equations
Given the following system of inequalities, find the answer below that does NOT satisfy the system.
To be a solution to the system, the point must satisfy BOTH inequalities. All five points satisfy the inequality . On the other hand, does not satisfy .
Example Question #21 : Systems Of Equations
20 fifth graders attended a birthday party. Each child got to choose between playing minature golf, which cost $4, or bowling, which cost $6. The total cost of the party was $96. How many children playing minature golf?
12
15
14
8
10
12
Let x equal the number of children that played minature golf and let y equal the number of children who bowled.
Based on that, we can conclude that:
and
Let's solve for x in the first equation by subtracting y from each side.
Now, let's substitute that expression for x in the second equation:
Now, distribute the 4:
Simplify:
Subtract 80 from both sides:
Divide both sides by 2:
Therefore, 8 children bowled. By substituting y into the first equation, we know that
Solve for x by subtracting 8 from both sides:
Example Question #22 : Systems Of Equations
At what point will the lines and intersect?
(1, 6)
(6, –1)
(1, –6)
(6, 1)
(–1, 6)
(1, 6)
In order to find this point, we must find the solution to the system of equations. we will use substitution, setting the two expressions for y equal to one another.
Then we plug this value back into either expression for y, giving us
So the point is (1, 6).
Example Question #25 : Systems Of Equations
Let be the point of intersection between the lines given by the equations and . What is the slope of the line that passes through and the origin?
In order to solve this system of equations, it will probably be best to use the elimination method, in which we add or subtract two equations. In general, if , and , then . In other words, we can combine equations.
We need to solve the following equations:
We want to look for a way to combine these two equations that will eliminate at least one variable. If, for example, we multiplied the first equation by and then added this to the second equation, we could get rid of the terms. Let's multiply the first equation by . Remember, we must multiply both sides.
Distribute the .
We can now add to the equation . The sum of the left sides of each equation will equal the sum of the right sides.
We can simplify both sides. Notice that the terms on the left disappear, leaving only terms.
Divide both sides by 3.
.
Now that we have , we can go back to either of our original two equations, substitute the value of we obtained, and solve for . Let's use the equation .
Substitute for .
Add to both sides. We will need to rewrite 4 with a denominator of 3.
Divide by 2 on both sides. When dividing a fraction, we simply multiply by its reciprocal.
Point , which is the intersection of the lines, must have the coordinates .
The question ultimately asks for the slope of the line passing through and the origin. We can use the equation of the slope between two points with coordinates and .
slope =
The answer is .
Example Question #23 : Systems Of Equations
Where do the lines and intersect?
Finding the intersection of two lines is the same as solving simultaneous equations. Here, both equations are already solved for , so the right sides of both equations are set equal to each other. Solving for results in a value of 11. Setting equal to 11 in either of the original equations gives a value of 27.
Example Question #242 : Algebra
At a carnival, hamburgers cost $4 while hot dogs cost $2. Becky has to buy 18 items for her students. She spent a total of $48. How many hamburgers did she buy?
6
12
10
8
6
Let x equal the number of hamburgers and y equal the number of hotdogs.
Solve for y in the first equation.
Substitute that solution into the second equation.
Example Question #24 : Systems Of Equations
This year, Amy is 3 times older than Jackie. In 6 years, Amy will be 2 times older than Jackie. How old is Jackie today?
18
6
12
10
6
Let Amy's current age be equal to A and Jackie's age be equal to J.
Therefore, and
Substitute the first equation into the second.
Therefore, today Jackie is 6 years old.