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If P is an odd integer and (P^2 + Q * R) is an even intege

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If P is an odd integer and (P^2 + Q * R) is an even intege [#permalink]

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New post 30 Jun 2017, 07:06
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If P is an odd integer and (P^2 + Q * R) is an even integer, then which of the following must be true?

A. either Q or R is an odd integer
B. either Q or R is an even integer
C. both Q and R are odd integer
D. both Q and R are even integers
E. nothing can be concluded
[Reveal] Spoiler: OA

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Re: If P is an odd integer and (P^2 + Q * R) is an even intege [#permalink]

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mkrishnabdrr wrote:
If P is an odd integer and (P^2 + Q * R) is an even integer, then which of the following must be true?

A. either Q or R is an odd integer
B. either Q or R is an even integer
C. both Q and R are odd integer
D. both Q and R are even integers
E. nothing can be concluded


P^2 + QR = even

odd^2 + QR = even

odd + QR = even

QR = even - odd = odd.

If Q and R are integers, then both must be odd but we don't know that. So, they might not be integers at all (say \(Q=R=\sqrt{3}\)), which makes E the answer.

Answer: E.
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Re: If P is an odd integer and (P^2 + Q * R) is an even intege [#permalink]

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New post 30 Jun 2017, 08:06
mkrishnabdrr wrote:
If P is an odd integer and (P^2 + Q * R) is an even integer, then which of the following must be true?

A. either Q or R is an odd integer
B. either Q or R is an even integer
C. both Q and R are odd integer
D. both Q and R are even integers
E. nothing can be concluded


We have 3 variable - P , Q and R

Given (P^2 + Q * R) = Even and P^2 = Odd

So, P = Odd

So, We can conclude that Q*R = Even, because Even*Even = Even & Odd*Even = Even

So, Q = Odd/Even & R = Odd/Even

Thus, we can not definitely conclude any value for Q or R, answer will be (E)
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Re: If P is an odd integer and (P^2 + Q * R) is an even intege [#permalink]

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New post 09 Aug 2017, 07:53
mkrishnabdrr wrote:
If P is an odd integer and (P^2 + Q * R) is an even integer, then which of the following must be true?

A. either Q or R is an odd integer
B. either Q or R is an even integer
C. both Q and R are odd integer
D. both Q and R are even integers
E. nothing can be concluded


P is an odd integer
(P^2 + Q * R) is an even integer

P^2 is also an odd integer... So, for (P^2 + Q * R) to be an even integer, Q*R must be odd integer.
Now Q*R can be odd in two cases.

1st : Both are integers : In this case Q and R both are odd integers.

2nd : One of them is integer and other is fraction : In this case the first integer may be odd or even and second integer is a fraction.

So, Nothing can be concluded about Q & R in terms of being odd or even or integral form.

Answer E

This is a very tricky question. People, including me, get caught in the trap and mark the wrong answer as C. Be very careful while reading such questions... A simple mistake will cost your marks. Finally don't forget to appreciate.
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Re: If P is an odd integer and (P^2 + Q * R) is an even intege   [#permalink] 09 Aug 2017, 07:53
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