ds test4 #23

dunkin77 · Posted: Thu Apr 05, 2007 6:03 pm Post subject: ds test4 #23

Hi,

The answer is C) but I am not too sure why A) is a necessary information - please explain... thanks!

If x and y are positive integers and x is a multiple of y, is y = 2?
(1) y ≠ 1
(2) x + 2 is a multiple of y.

jayhawk2001 · Posted: Thu Apr 05, 2007 10:05 pm Post subject:

We are given x = my

1 - insufficient. Just knowing y != 1 does not help

2 - insufficient. We have x+2 = ny. Subtracting the 2 equations,
we get

x+2 - x = ny - my
or (n-m)y = 2

Since we are dealing with +ve integers here, we have 2 possibilities

n-m = 2, y = 1
n-m = 1, y = 2

Taking 1 and 2 together, we know that y!=1, so it boils down to
n-m = 1, y = 2

Hence C

dunkin77 · Posted: Thu Apr 05, 2007 10:43 pm Post subject:

Ohh very clear - thank you!! Very Happy