If a and b are integers such that a > b > 1, which of the following cannot be a multiple of either a or b?

(A) a - 1

(B) b + 1

(C) b - 1

(D) a + b

(E) ab

I understand why (b-1).[Logically it is absolutely right] but it doesn’t seem to follow when a=8 b=5 or a=20,b=15, for that matter. Please correct me if I’m wrong.

**Thank you in advance!**

a = 8 , b =5

C = b-1 = 5-4 =4

Multiple of 8 = 8 ,16,24 etc .

Now, 4 is not a multiple of 8, 8 is a multiple of 4 and questioned asked multiple of (for our case: a=8or b=5)

Multiple of 4 = 4,8,12 etc

2 Likes

Yeah, true! but option D) a+b =8+5 =13 isn’t multiple of either a or b. so I thought that could have been an anomaly. I think they should have used MUST NOT instead of CANNOT ?