Concept on Number Properties

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by GMATGuruNY » Fri Aug 16, 2013 3:30 am
If p/q < 1, and p and q are positive integers, which of the following must be greater than 1 ?

A) sqrt (p/q)
B) p/q^2
C) p/2q
D) q/p^2
E) q/p
Since q>0, we can safely multiply each side by q:
p/q < 1
p < q.

Given this constraint, try to show that 4 of the 5 answer choices do NOT have to be greater than 1.

Plug p=2 and q=3 into the answer choices.
If an answer choice yields a result not greater than 1, eliminate the answer choice.
A) √(p/q) = √(2/3) = √2/√3 ≈ 1.4/1.7 = 14/17.
B) p/q² = 2/3² = 2/9.
C) p/2q = 2/(2*3) = 1/3.
D) q/p² = 3/2² = 3/4.
Eliminate A, B, C and D.

The correct answer is E.

The OA indicates that q/p > 1.
Since p>0, we can safely multiply each side by p:
q/p > 1
q > p
p < q.
Given our rephrase of the question stem, it must be true that p < q.
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by Brent@GMATPrepNow » Fri Aug 16, 2013 6:00 am
ProGMAT wrote:If p/q<1, and p and q are positive integers, which of the following must be greater than 1?
(A) (p/q)sq. root
(B) p/(q sq.)
(C) p/2q
(D) q/(p sq.)
(E) q/p

OA: E
IMPORTANT: For questions like this, where you need to test each answer choice, the test-makers will often make D or E the correct answer (because they want to eat up your valuable time :-)). So, in these situations, always begin with E and work your way up.

E. Is q/p > 1?
Well, we're told that p/q < 1.
Since q is a positive integer, we can multiply both sides by q to get: p < q
Since p is a positive integer, we can now divide both sides by p to get: 1 < q/p
So, answer choice E must be true.

Answer: E

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Brent
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