Data Sufficiency

If x and y are positive integers, is xy a multiple of 8?

(1) The greatest common divisor of x and y is 10
(2) The least common multiple of x and y is 100

OA: C

These questions are my biggest weakness.

lachlanc wrote:If x and y are positive integers, is xy a multiple of 8?

(1) The greatest common divisor of x and y is 10
(2) The least common multiple of x and y is 100

OA: C

These questions are my biggest weakness.

Okay this one goes to your flash card:

X x Y = (LCM of X and Y) x (GCF of X and Y)

100x10 = 1000

divisible by 8

Hence, C

1) let x=10a, y=10b (since GCD =10)
or xy=100ab, cant say if 100ab is a multiple of 8, not sufficient

2) LCM of x and y=100 or xy=100/(common factors between x and y if any). we do not know what are the common factors, hence not sufficient

combining: xy=product of LCM*GCD (product of 2 numbers =GCD*LCM)
or xy=1000, divisible by 8, hence C

Thanks guys.