saghosh1 wrote:
QuantMadeEasy wrote:
If x + y is odd, which of the following could be true?
(I) xy is even
(II) xy is odd
(III) x/y is even
A. I only
B. II only
C. III only
D. I and II
E. I and III
When we are talking about a "could be true" question is PS, do we consider the option as correct even if it satisfies one condition?
For eg: In option (III), x/y can be even only when x is even and a multiple of y, and y is odd (6/3=2).
If y is odd and x is even, then it will be a fraction.
For this particular reason I marked my answer as
A. I only but the OA marked is
E. I and III"MUST BE TRUE" questions:
These questions ask which of the following
MUST be true, or which of the following is
ALWAYS true for ALL valid sets of numbers you choose. Generally for such kind of questions
if you can prove that a statement is NOT true for one particular valid set of numbers, it will mean that this statement is not always true and hence not a correct answer.
So,
for "MUST BE TRUE" questions plug-in method is good to discard an option but not 100% sure thing to prove that an option is ALWAYS true.
As for "COULD BE TRUE" questions:
The questions asking which of the following
COULD be true are different:
if you can prove that a statement is true for one particular set of numbers, it will mean that this statement could be true and hence is a correct answer.
So,
for "COULD BE TRUE" questions plug-in method is fine to prove that an option could be true. But here, if for some set of numbers you'll see that an option is not true, it won't mean that there does not exist some other set which will make this option true.