SAT Math : How to solve for a variable as part of a fraction

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #3241 : Sat Mathematics

Solve:

 \(\displaystyle \frac{4}{11}x + 3 = 15\)

Possible Answers:

\(\displaystyle x = 29\)

\(\displaystyle x = \frac{48}{11}\)

\(\displaystyle x = 37\)

\(\displaystyle x = 39\)

\(\displaystyle x = 33\)

Correct answer:

\(\displaystyle x = 33\)

Explanation:

We want to isolate the x. First, we take away 3 from both sides. Then we have: 

\(\displaystyle \frac{4}{11}x = 12\)

 

To get x by itself, we multiply by the reciprocal on both sides. 

Then, we have: 

\(\displaystyle x = 12 \times \frac{11}{4} = \frac{12}{1}\times\frac{11}{4} = \frac{132}{4} = 33\)

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

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

Possible Answers:

none of these

3/38

7/12

9/114

38/3

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

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

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

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

None

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 #2 : 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:

\(\displaystyle 12\)

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

\(\displaystyle 18\)

\(\displaystyle 6\)

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

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

Solve for x:

\(\displaystyle \frac{x-67}{-x+85}=\frac{3}{6}\)

Possible Answers:

\(\displaystyle \frac{9}{657}\)

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

\(\displaystyle 657\)

\(\displaystyle \frac{9}{1}\)

\(\displaystyle 73\)

Correct answer:

\(\displaystyle 73\)

Explanation:

In order to solve for x, you must cross multiply the ratio first. They will be equal to each other. \(\displaystyle 6(x-67)=3(-x+85)\)

\(\displaystyle 6x-402=-3x+255\), you then can add 3x to both sides and 402 to both sides as well. You are left with:

\(\displaystyle 9x=657\) divide both sides by 9 to get the final answer:

\(\displaystyle x=73\)

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