Hi ashish,
In Roman Numeral questions, usually the fastest way to get to the correct answer is to do the opposite of what the question asks. Here, we're asked what "MUST be true" so we'll try to prove the opposite (what is NOT always true and WHY). These questions are usually best solved by TESTing VALUES.
We're told that Y CANNOT be 3 and that 3X/Y is a PRIME number GREATER than 2...
I. X=Y
Many of the TESTs that you might come up with will involve making X and Y the same value (1 and 1, 2 and 2). In these situations, the fraction will always equal 3 (which IS a prime number greater than 2). The key to disproving THIS Roman Numeral is to try to make the prime number something OTHER than 3.
If X = 10 and Y = 6, then 3X/Y = 5 (which IS also a prime number greater than 2).
Roman Numeral I is NOT always true.
II. Y = 1
We can use the example that we used in Roman Numeral I to disprove this one too.
Roman Numeral II is NOT always true.
III. X and Y are prime numbers
Again, we can use the prior example to disprove this Roman Numeral
Roman Numeral III is NOT always true.
Final Answer: A
GMAT assassins aren't born, they're made,
Rich
