read more at:http://mathforum.org/library/drmath/view/60913.html
I don't know if thats the GMAT official standpoint.
page 108 of OG:
if x and y are integers and x doesnt = 0, then x is a divisor of y provided that y=xn for some integer n. In this case, y is also said to be divisible by x or to be a multiple of x. so "y" is a multiple if a nonzero integer times another integer = y.
28=7*4 7 is a divisor/factor of 28 and 28 is a multiple of 7.
it doesn't say that any of the integers have to be unique, so:
0=333*0 etc.. etc..
that is how I am interperting it.
zero is a multiple of every # and every number is a multiple of zero