Data Sufficiency and Square Roots

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vongdn: Senior | Next Rank: 100 Posts; Posts: 52; Joined: Sat Aug 14, 2010 9:24 pm

by vongdn » Wed Sep 29, 2010 9:46 pm

In Data Sufficiency questions, lets say you need to find a particular value.....If in one of the options you can simplify it down to the square root, does it mean that the option is insufficient, because a square root can either be negative or positive?

example:

Find n = ?
(1) n = square root of 4 -->

Since the square root of 4 can be 2 or -2, does that mean the answer is insufficient because you do not have enough information to figure out whether it is 2 or -2?

Thanks

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Source: Beat The GMAT — Data Sufficiency | Wed Sep 29, 2010 9:46 pm

shovan85: Community Manager; Posts: 991; Joined: Thu Sep 23, 2010 6:19 amFollowed by: 24 members; Location: Bangalore, India; Thanked: 146 times

by shovan85 » Wed Sep 29, 2010 9:55 pm

Yes vongdn. The option is insufficient, however, if the option or question has not mentioned anything about positive or negative square root.

For example if in the question you have been given a square(geometry). And in option you have been given the area of the same then the side of the square has to be positive.

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Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pmFollowed by: 88 members; Location: Milpitas, CA; Thanked: 447 times

by Rahul@gurome » Wed Sep 29, 2010 10:17 pm

In GMAT, we only consider the positive square root.
So if n = sqrt(4), the value of n is only 2 and not -2.
However had it been given that n^2 = 4, then we would have to take that n has two values 2 and -2.
Hence statement (1) is sufficient in this case.

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vongdn: Senior | Next Rank: 100 Posts; Posts: 52; Joined: Sat Aug 14, 2010 9:24 pm

by vongdn » Wed Sep 29, 2010 10:57 pm

Rahul@gurome wrote:In GMAT, we only consider the positive square root.
So if n = sqrt(4), the value of n is only 2 and not -2.
However had it been given that n^2 = 4, then we would have to take that n has two values 2 and -2.
Hence statement (1) is sufficient in this case.

Thanks for the clarification, then in the case that n^2 = 4, and we are trying to find the value of n, would that mean that the data is insufficient.

ie. Find the value of n...

(1) n^2 = 4 --> Insufficient.

Thanks

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alivapriyada: Master | Next Rank: 500 Posts; Posts: 146; Joined: Fri Jun 25, 2010 3:42 amFollowed by: 1 member; Thanked: 3 times; GMAT Score:560

by alivapriyada » Thu Sep 30, 2010 2:36 am

vongdn wrote:
Rahul@gurome wrote:In GMAT, we only consider the positive square root.
So if n = sqrt(4), the value of n is only 2 and not -2.
However had it been given that n^2 = 4, then we would have to take that n has two values 2 and -2.
Hence statement (1) is sufficient in this case.
Thanks for the clarification, then in the case that n^2 = 4, and we are trying to find the value of n, would that mean that the data is insufficient.

ie. Find the value of n...

(1) n^2 = 4 --> Insufficient.

Thanks

yes you are correct.
for GMAT
n^2=4 ----> insufficient.

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