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

Question

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

Bunuel · Accepted Answer

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.

Abhishek009 · Answer

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)

shashankism · Answer

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.

JeffTargetTestPrep · Answer

Solution:

Since P is odd, P^2 is also odd.In order for P^2 + Q * R to be even, Q * R must be odd, since odd + odd = even. If we knew that both Q and R were integers, then necessarily both Q and R would have to be odd. However, Q could be 2 and R could be 1/2, in which case the product Q * R = 2 x 1/2 = 1 is still an odd integer. Therefore, we cannot conclude anything about the parity of Q and R. Thus, the answer is E.

Answer: E

EMPOWERgmatRichC · Answer

Hi All,

We're told that If P is an ODD integer and (P^2 + Q * R) is an EVEN integer. We're asked which of the following MUST be true. This question can be solved with a mix of Number Properties and TESTing VALUES.

To start, since P is ODD, we know that P^2 will also be ODD (since ODD^2 = ODD). 
For (ODD + Q * R) to be EVEN, we know that (Q * R) must also be ODD. However we do NOT know whether Q and R are integers or not...

IF Q=1 and R=1, then all 3 variables are ODD. 
IF Q=2 ad R = 1/2, then the 3 variables include one ODD, one EVEN and one non-integer.

Thus, none of the first 4 answers is always going to be true.

Final Answer:  E

GMAT assassins aren't born, they're made, 
Rich

sanjayparihar16 · Answer

Hi Abhishek,

I think there is some typo in the end of your answer. Q*R is not even, it is odd.

Regards,
Sanjay

Aabhash777 · Answer

Suppose P = 1, then 
(P^2) + (Q*R) = Even
(1^2) + (Q*R) = Even
1 +(Q*R) = Even
Q*R = Even - 1 = Odd

Since, Q and R are not integers, now there are three cases:

I. 5 * 1/5 = 1 (odd) here only Q or R is odd
II. 5 * 3 = 15 (odd) here both Q and R are odd
III. 3/5* 5/3 = 1 (odd) here neither Q nor R is odd

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

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards