If A-B = B-C = 20, then 3A + 2B + C =? Analytically, if A-B = B-C = 20 and a-c = 40, then A-B, B-C and a-c are not multiples of 3, that is, a, B and C have a number that is multiples of 3. Why?

If A-B = B-C = 20, then 3A + 2B + C =? Analytically, if A-B = B-C = 20 and a-c = 40, then A-B, B-C and a-c are not multiples of 3, that is, a, B and C have a number that is multiples of 3. Why?

∵ A-B = B-C = 20, ∵ C, B and a are arithmetic sequences with 20 as tolerance, ∵ a-c = 40. Obviously, 20 and 40 are not multiples of 3, ∵ A-B, B-C and a-c are not multiples of 3