Question

The largest no divieds by 70 and 125 give reminder 5 and 8

Answer 1

The first one is:
70 = 13x5 + 5
125 = 13x9 + 8
So that's a possible answer to the "largest."

The second one works for 70 but
125 = 65 + 60 so it doesn't work for 125.

The 3rd and 4th all have quotient of 0 and so the remainders are 70 and 125.

So 13 is the only one that works, and the answer is A.