Source: Revised GRE PDF 1st Ed. Section 6: Math; #21 (p. 90)


The quantities S and T are positive and

The quantities S and T are positive and are related by the equation S = k/T, where k is a constant. If the value of S increases by 50 percent, then the value of T decreases by what percent? 25%, 33 1/3%, 50%, 66 2/3%, 75%

3 Explanations


Darnell Billups

I got this one wrong on the practice test. I did all the math right and had no issues getting to 66 2/3%. However, I did not take the next step and answer for what I was asked to solve for in the question. I'm starting to notice that the math principles are easier to relearn from HS, however, it's the difficulty of getting around how they write problems. The problems are intentionally misleading and phrased to make it difficult to find easily what they are asking you to solve for. Next time, I'm going to spend a few more seconds to make a clear picture of what they want from me. I'll also look at words in the final part of the question like increase, decrease, etc, to make me stop and think. The other thing I saw with this is that I started out with eliminating answer choice C (50%). If I had no idea to solve to this one, I would have know that C was not the answer because it is simply recycling information from the word problem. ETS does this to catch people in my opinion.

Oct 12, 2016 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Darnell! Thanks for sharing your insight :) I agree that it's important to really understand what is being asked so that you don't fall into potential traps. Thanks again for your message :D Happy studying!

Oct 14, 2016 • Reply


Vish .

There is a pattern increase by 1/x% implies a decrease in (x+1)%.

I mean an increase in 50% implies a dec in T by 33.33%

similarly inc by 25% means a dec by 20%

similarly inc by 16.66% means a dec by 14.28%...

Nov 27, 2015 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Vish,

Thanks for your comment :) There is definitely a pattern in this question!

However, I'm not exactly sure what (1/x%) represents. An increase of 50% is means that the new value is 1.5 times greater than the original.

It turns out that S and T are inversely proportional. In other words, S is proportional to 1/T. So, when S changes by a factor of x, then T will change by a factor of 1/x. And we can express a decrease of T as (1-1/[change in S]).

If S increases by 50% (a factor of 1.5), T will change by a factor of 1/1.5 = 2/3. The new value of T will be 2/3 of the original value, which is a decrease of 1-2/3 = 1/3 = 33.3%.

I hope this helps!

-Cydney :)

Dec 2, 2015 • Reply

Hey, vish this is fixed pattern above you mention there!

Apr 29, 2016 • Reply


Gravatar Chris Lele, Magoosh Tutor

Sep 26, 2012 • Comment

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