Bunuel wrote:

What is the total weight of four crates?

(1) The average weight of the four crates is 200 pounds.

(2) The total weight of two of the crates is exactly three times the total weight of the other two crates.

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question, and then recheck the question.

We can modify the question in the following way.

Assume a, b, c, and d are weights of four crates.

The question asks for the value of a + b + c + d.

a + b + c + d = ?

Condition 1) :

( a + b + c + d ) / 4 = 200 ⇔ a + b + c + d = 800

Condition 1) is same as the question.

It is sufficient.

Condition 2) :

a + b = 3( c + d ).

This equation doesn't give any information about the sum of a, b, c and d.

Thus condition 2) is not sufficient.

Therefore, the answer is A.

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