What is the perimeter of a rectangle with length L...

[BTGmoderatorLU]

What is the perimeter of a rectangle with length L and width W?

1) L - W = 15
2) L + W = 35

The OA is B.

Please, can any expert assist me with this DS question? I don't have it clear why that is the correct answer? I appreciate if any explain it for me. Thanks.

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Hi LUANDATO,

We're asked for the perimeter of a rectangle with a length of L and a width of W. You can use a mix of logic and TESTing VALUES to get to the correct answer. Regardless of your approach though, you'll need the formula for perimeter of a rectangle:

Perimeter = 2L + 2W

1) L - W = 15

Fact 1 doesn't provide us with the necessary information to determine the value of 2L + 2W. You can also TEST VALUES to prove the inconsistency:
IF....
L=16, W=1, then the perimeter is 32 + 2 = 34
L=17, W=2, then the perimeter is 34 + 4 = 38
Fact 1 is INSUFFICIENT

2) L + W = 35

Fact 2 gives us the value of L+W. If we double this equation, we'll have...
2L + 2W = 70 and that is the exact value that we're trying to determine. You can also TEST VALUES - and you'll find that the answer is ALWAYS 70.
Fact 2 is SUFFICIENT

Final Answer: B

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