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sgoll
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Gmatprep- prime numbers 22 Feb 2007, 21:47
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Can anyon explain this please.



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Gmatprep- prime numbers 22 Feb 2007, 22:00
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I would say D.

We know (or at least I think), that p or q has to equal 5. D is the only answer that would definetly yield 25, therefore D is the only answer that works.
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Gmatprep- prime numbers 22 Feb 2007, 23:26
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I plugged in two easy numbers that satisfy the first statement, p=3 and q=5, then went through the answers one by one. note p=5 and q=3 also yields a multiple of 5.

if p=3 A is out.
if q=3 B is out.
C is out either way.
D works whether p=3 and q=5 or viceversa so I stopped.

Answer: D.
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Gmatprep- prime numbers 23 Feb 2007, 10:45
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N = 5K , K IS +VE INTIGER,

5K = P^2Q ie either p or q .............or both could be a multiple of 5

for any p.q combination to be a multiple of 25

we have to satisfy the assumption (either p or q .............or both could be a multiple of 5) through its worst case scenario which is only q or only p is a multiple of five thus we need a square of each at least to make sure that we will end up with a 25 multiple

thus p^2*q^2 satisfies the worst case scenario



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