ACT Math : Algebra

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #2 : How To Solve For A Variable As Part Of A Fraction

Solve for \(\displaystyle x\):

\(\displaystyle \frac{x+1}{4}-\frac{x}{3}=6\)

Possible Answers:

\(\displaystyle x=-69\)

\(\displaystyle x=26\)

\(\displaystyle x=42\)

\(\displaystyle x=-72\)

\(\displaystyle x=60\)

Correct answer:

\(\displaystyle x=-69\)

Explanation:

Solve for x:

\(\displaystyle \frac{x+1}{4}-\frac{x}{3}=6\)

Step 1: Find the least common denominator, \(\displaystyle 12\), and adjust the fractions accordingly:

\(\displaystyle \left (\frac{3}{3} \right )\cdot \left ( \frac{x+1}{4} \right ) - \left ( \frac{4}{4} \right )\cdot \left ( \frac{x}{3} \right )=6\)

\(\displaystyle \left ( \frac{3x+3}{12} \right )-\left ( \frac{4x}{12} \right )=6\)

Solve for \(\displaystyle x\):

\(\displaystyle \frac{3x+3-4x}{12}=6\)

\(\displaystyle 3x+3-4x=72\)

\(\displaystyle -x=69\)

\(\displaystyle x=-69\)

 

Example Question #65 : Algebraic Fractions

If \(\displaystyle \frac{6}{x}=\frac{9}{19}\) , then what is the value of \(\displaystyle x\)?

Possible Answers:

38/3

none of these

9/114

7/12

3/38

Correct answer:

38/3

Explanation:

cross multiply:

(6)(19) = 9x

114=9x

x = 38/3

Example Question #1 : How To Solve For A Variable As Part Of A Fraction

\dpi{100} \small \frac{4 }{x} = \frac{2}{25}\(\displaystyle \dpi{100} \small \frac{4 }{x} = \frac{2}{25}\)

Find x.

Possible Answers:

\dpi{100} \small 50\(\displaystyle \dpi{100} \small 50\)

\dpi{100} \small 0.25\(\displaystyle \dpi{100} \small 0.25\)

None

\dpi{100} \small \frac{8}{25}\(\displaystyle \dpi{100} \small \frac{8}{25}\)

\dpi{100} \small \frac{25}{8}\(\displaystyle \dpi{100} \small \frac{25}{8}\)

Correct answer:

\dpi{100} \small 50\(\displaystyle \dpi{100} \small 50\)

Explanation:

Cross multiply:

\dpi{100} \small 4 \times 25 = 2x\(\displaystyle \dpi{100} \small 4 \times 25 = 2x\)

\dpi{100} \small 100 = 2x\(\displaystyle \dpi{100} \small 100 = 2x\)

\dpi{100} \small x = 50\(\displaystyle \dpi{100} \small x = 50\)

Example Question #1 : How To Solve For A Variable As Part Of A Fraction

The numerator of a fraction is the sum of 4 and 5 times the denominator. If you divide the fraction by 2, the numerator is 3 times the denominator. Find the simplified version of the fraction.

Possible Answers:

\(\displaystyle \frac{1}{3}\)

\(\displaystyle 12\)

\(\displaystyle 6\)

\(\displaystyle 18\)

\(\displaystyle \frac{1}{2}\)

Correct answer:

\(\displaystyle 6\)

Explanation:

Let numerator = N and denominator = D.

According to the first statement, 

N = (D x 5) + 4.

According to the second statement, N / 2 = 3 * D. 

Let's multiply the second equation by –2 and add itthe first equation:

–N = –6D

+[N = (D x 5) + 4]

=

–6D + (D x 5) + 4 = 0

–1D + 4 = 0

D = 4

Thus, N = 24.

Therefore, N/D = 24/4 = 6.

Example Question #1 : How To Solve For A Variable As Part Of A Fraction

Solve the following equation for the given variable:

\(\displaystyle \frac{2}{3x}=4\)

Possible Answers:

\(\displaystyle x = \frac{3}{4}\)

\(\displaystyle x = \frac{8}{3}\)

\(\displaystyle x = \frac{1}{5}\)

\(\displaystyle x = \frac{1}{6}\)

\(\displaystyle x = \frac{3}{2}\)

Correct answer:

\(\displaystyle x = \frac{1}{6}\)

Explanation:

To solve this equation we have to multiply both sides by the denominator to get rid of the fraction.

Doing this yields

\(\displaystyle 2 = 12x\) 

Then to solve the last step is to isolate the variable by dividing both sides by 12.
Thus, 

\(\displaystyle x = \frac{2}{12}=\frac{1}{6}\).

Example Question #5 : How To Solve For A Variable As Part Of A Fraction

For what value of \(\displaystyle x\) is the equation \(\displaystyle \frac{4}{12}=\frac{5}{x}\)  true?

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 14\)

\(\displaystyle 3\)

\(\displaystyle 12\)

\(\displaystyle 15\)

Correct answer:

\(\displaystyle 15\)

Explanation:

When the equation is cross multiplied, it becomes

\(\displaystyle \\ 4\cdot x=5\cdot 12 \\4x = 60\).

Hence,

\(\displaystyle x =\frac{60}{4}\), or \(\displaystyle x=15\)

Example Question #4 : How To Solve For A Variable As Part Of A Fraction

Solve the following equation for \(\displaystyle x\):


\(\displaystyle \frac{36}{5x} = 4\).

Reduce any fractions in your final answer.

Possible Answers:

\(\displaystyle x = 5\)

\(\displaystyle x = \frac{5}{9}\)

\(\displaystyle x = 3\)

\(\displaystyle x = \frac{9}{5}\)

\(\displaystyle x = \frac{36}{20}\)

Correct answer:

\(\displaystyle x = \frac{9}{5}\)

Explanation:

To solve an equation with a variable in a fraciton, treat the denominator as a constant value and multiply both sides of the equation by the denominator in order to eliminate it.
\(\displaystyle \\5x * \left(\frac{36}{5x}\right) = 4 * 5x\\ \newline 36 = 20x \newline \newline \frac{36}{20} = x \\ \newline \frac{9}{5}= x\)

Example Question #1 : How To Solve For A Variable As Part Of A Fraction

Solve for \(\displaystyle x\)\(\displaystyle \frac{x}{12}=3\)

Possible Answers:

\(\displaystyle 4\)

\(\displaystyle \frac{1}{36}\)

\(\displaystyle \frac{1}{3}\)

\(\displaystyle 24\)

\(\displaystyle 36\)

Correct answer:

\(\displaystyle 36\)

Explanation:

To find the answer, multiply the right side by \(\displaystyle 12\). The result is \(\displaystyle 36=x\).

Example Question #61 : Algebraic Fractions

Solve for \(\displaystyle x\):

\(\displaystyle \frac{3}{4}=\frac{5x+10}{20}\)

Possible Answers:

\(\displaystyle 1\)

\(\displaystyle 4\)

\(\displaystyle 5\)

\(\displaystyle 2\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 1\)

Explanation:

To solve this problem you must cross mutiply, then set the two equations equal to each other. Your first equation is\(\displaystyle 3\left ( 20\right )\), your second is \(\displaystyle 4\left ( 5x+10\right )=20+40\). This gives you \(\displaystyle 60=20x+40\). Subtract \(\displaystyle 40\) from both sides, so you have \(\displaystyle 20=20x\), divide by \(\displaystyle 20\) on both sides and you have \(\displaystyle x=1\).

Example Question #11 : How To Solve For A Variable As Part Of A Fraction

Solve for \(\displaystyle x\):

\(\displaystyle \frac{14}{x+3}=\frac{2}{3}\)

Possible Answers:

\(\displaystyle 19.5\)

\(\displaystyle 18\)

\(\displaystyle 20\)

\(\displaystyle 16\)

Correct answer:

\(\displaystyle 18\)

Explanation:

Cross multiply: \(\displaystyle 42=2(x+3)\)

Distribute: \(\displaystyle 42=2x+6\)

Solve for \(\displaystyle x\)\(\displaystyle 36=2x\)

\(\displaystyle 18=x\)

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