(x/a)*100 =b

let a = 100 and x = 10 then b =10
in this case
a is = 100/x times b

now ,

let a=150 and x =50 then b = 75
in this case
a is =100/x times b

for confirmation

let a =200 and x =30 then b = 120
in this case
a is again = 100/x times b

so E 100/x

Given: x percent of a = b

\(a*(\frac{x}{100})=b\)

What we're being asked: a = b*(something in terms of x)

Rearrange our original equation

\(a=b*(\frac{100}{x})\)

Answer: E

We can check by testing values. When testing values, it's important to avoid values that might give false positives. You want numbers that are easy to work with, but will give you unique answers.
let a = 90 and x = 20, then b = 18

\(b*(\frac{100}{x}) = 18*(\frac{100}{20}) = 90\)

Checks out.

If instead I had chosen a = 100 and x = 10, then b = 10. Then b*10 = a, and both answers C and E could work. It's not always easy, but one should always try to choose numbers that will give different results for each answer choice.
_________________

Hi All,

This question is essentially a 'lift' of an OG question.

In the GMAT2016: PS Question 194 (page 180).
In the GMAT2015/OG13: PS Question 181 (page 177).

GMAT assassins aren't born, they're made,
Rich
_________________

Hi CounterSniper,

I think you mean in highlighted part that (x*a)/100 =b such that in you example (30*200)/100= 120

Those are almost the answer I chose and apparently why I got it wrong! x=10, a=200, b=20. C and E work for both.

Hi All,

Since some of posts have mentioned coming across more than one answer that 'matches' what you're looking for, we should take a moment to talk about how to AVOID choosing VALUES that will lead to those duplicate solutions.

Consider the 5 answer choices to this prompt:

A. 100x
B. 10x
C. x
D. 10/x
E. 100/x

What values of X will lead to a pair of 'matching' answers (hint: think about the numbers that appear in the 5 answer choices)?



Therefore, you should AVOID using these numbers when you TEST VALUES.

GMAT assassins aren't born, they're made,
Rich
_________________

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________