Question

is zero a multiple of 11?

Answer 1

Yes zero is a multiple of every number

Answer 2

An integer aa is a multiple of an integer bb means that ab=integerab=integer: so, as 0 divided by any integer (except zero itself) yields an integer then yes, zero is a multiple of every integer (except zero itself).

Also on GMAT when we are told that aa is divisible by bb (or which is the same: "aa is multiple of bb", or "bb is a factor of aa"), we can say that:
1. aa is an integer;
2. bb is an integer;
3. ab=integerab=integer.

Hope it helps.