Hi All,
This DS question, like many DS questions on Test Day, is meant to test the 'thoroughness' of your thinking. It's important to think about what you KNOW about the variables and what you DON'T know...
We're asked if the sum of 7X and 7Y is divisibly by 14. This is a YES/NO question. It's important to remember that we were NOT told anything about X and Y (maybe they're integers, but maybe they're not). TESTing VALUES will prove to be quite useful here.
1) X = Y
This Fact tells us that the two variables are equal to one another, but we don't know what they actually are.
IF...
X = Y = 1/2
Then 7(1/2) + 7(1/2) = 7 and the answer to the question is NO.
IF...
X = Y = 1
Then 7(1) + 7(1) = 14 and the answer to the question is YES.
Fact 1 is INSUFFICIENT
2) X and Y are both even integers
This Fact gives us a very specific restriction - X and Y are BOTH EVEN integers. With this restriction, ANY possible values that you choose for X and Y will lead to a total that is divisible by 14.
For example...
IF...
X = Y = 2
Then 7(2) + 7(2) = 28 and the answer to the question is YES.
IF...
X = 0
Y = 2
Then 7(0) + 7(2) = 14 and the answer to the question is YES.
IF...
X = -2
Y = -4
Then 7(-2) + 7(-4) = -42 and the answer to the question is YES.
Fact 2 is SUFFICIENT.
Final Answer:
GMAT assassins aren't born, they're made,
Rich
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