Data Sufficiency

aman88 wrote:Q. If a and b are positive integers, what is the value of a + b ?
(1) a/b = 5/8
(2) The greatest common divisor of a and b is 1.

My answer is E but the QA says C.

Thanks much.

(1) a/b = 5/8
a and b can take any values like: a = 5, b = 8 or a = 10, b = 16
Since a and b can take any value, so value of a + b also varies accordingly.
No definite answer; NOT sufficient.

(2) The greatest common divisor of a and b is 1 implies a and b can be any co-prime numbers; NOT sufficient.

Combining (1) and (2), we know that a and b have a common factor 1, and from statement 1, a = 5 and b = 8, which implies a + b = 5 + 8 = 13; SUFFICIENT.

The correct answer is C.