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perfect square test

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by CSASHISHPANDAY » Tue Jul 09, 2013 12:25 am
Squares of a number should always have one of these in Unit's place.
(1,4,9,5,6)
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by vipulgoyal » Wed Jul 10, 2013 1:47 am
thanks, I believe you skipped 0
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by Brent@GMATPrepNow » Wed Jul 10, 2013 5:30 am
vipulgoyal wrote:Which of the following cannot be a perfect square number?
A. 622,521
B. 99,856
C. 744,769
D. 426,408
E. 322,624

d
Aside: The GMAT will not assume that we know the meaning of "perfect square number." The phrase used it typically "square of an integer."

To answer the question we need only examine the units digit of the answer choices. Before we do that, however, we should make the following observations:
0² = 0
1² = 1
2² = 4
3² = 9
4² = 16
5² = 25
6² = 36
7² = 49
8² = 64
9² = 81

As we can see, any integer squared will have units digit 0, 1, 4, 5, 6 or 9

Answer: D,, since it has units digit 8, and 8 cannot be the units digit of the square of an integer.

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by send2dar » Sat Jul 13, 2013 5:53 am
CSASHISHPANDAY wrote:Squares of a number should always have one of these in Unit's place.
(1,4,9,5,6)
Good point, although 0 is missed in the above set. (Someone already pointed out this)
If units is 0, even hundreds should be 0... (for numbers with units digit 0). Except when the number itself is 0... but in that case it wouldn't be a GMAT test :)
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