Source: Official Guide for GMAT Review 2016 Data Sufficiency ; #163

1

If n is a positive integer and

If n is a positive integer and k=5.1x10, what is the value of k?

2 Explanations

1

Alan Man

Hi there, what about the fact that for S2, since we are taking the square root (and the square root does not appear in the question itself), then the square root could technically be both a positive and negative square root? Therefore not sufficient.

I am not sure what happens to a negative square root of an exponent - perhaps this would answer my question?

Apr 10, 2017 • Comment

Cydney Seigerman, Magoosh Tutor

Excellent question, Alan!

You're correct in your hunch that when we take the square root of k, we would end up with a positive and negative root. However, as we'll see below, S2 is still sufficient.

k^2 = 2.601 * 10^9

First, let's rewrite this value, getting rid of the decimal, and then we'll take the square root:

k^2 = 2.601 * 10^9 = 2601 * 10^6
k = sqrt(2601 * 10^6) = 51*10^3 or - 51*10^3

So, initially, we get two values for k. However, we're told in the prompt that k is positive, so we know that k = 51*10^3. Therefore S2 is sufficient :)

Hope this helps :)

Apr 12, 2017 • Reply

1

Gravatar Mike McGarry, Magoosh Tutor

Aug 18, 2015 • Comment

Add Your Explanation

You must have a Magoosh account in order to leave an explanation.

Learn More About Magoosh

Official GMAT Material

Official Guide for GMAT Review 2016

Official Guide for the GMAT 2015 14th Ed.

Official Guide for the GMAT 13th Ed.

Official Guide for the GMAT 12th Ed.

Revised GRE PDF 2nd Ed.


Section 6.3 Data Sufficiency

Improve Your Score

Magoosh GMAT is an affordable online course for studying the GMAT.

Learn More About Magoosh

Share Post

Email

Facebook