GHong14 wrote:If a and b are both single-digit positive integers, is a + b a multiple of 3?

(1) The two-digit number "ab" (where a is in the tens place and b is in the ones place) is a multiple of 3.
(2) a - 2b is a multiple of 3.

Statement 1: From the rule of divisibility by 3, we can easily conclude that if the two-digit number "ab" (where a is in the tens place and b is in the ones place) is a multiple of 3, then (a + b) is also a multiple of 3.

Sufficient

Statement 2: a - 2b is a multiple of 3
Now we can write (a - 2b) as (a + b - 3b).
Thus (a + b - 3b) is a multiple of 3, which is obtained by subtracting 3b (which is also multiple of 3) from (a + b).
Hence, (a + b) is also a multiple of 3.

Sufficient

The correct answer is D.