# If the operation is defined for all integers a and b by a@b = a + b – ab, which of the following statements must be true for all integers a, b and c? GMAT Explanation

If the operation is defined for all integers a and b by a@b = a + b – ab, which of the following statements must be true for all integers a, b and c?

I. a@b = b@a

II. a@0 = a

III. (a@b)@c = a@(b@c)

(A) I only

(B) II only

(C) I and II only

(D) I and III only

(E) I, II and III

**Correct Answer:** E