Rohan says adding two 3-digit numbers always gives a 3-digit answer

Why

Rohan has probably tried a few small examples — 123 + 234 = 357, still 3 digits — and assumed it always works out that way. But the sum of two 3-digit numbers can land anywhere between 100 + 100 = 200 (3 digits) and 999 + 999 = 1998 (4 digits), so whether the answer has 3 or 4 digits depends entirely on which two numbers you pick. Test it: 111 + 222 = 333 is 3 digits, but 700 + 800 = 1500 is 4 digits — both are 3-digit-plus-3-digit sums. His sister is right: the answer can be 3 or 4 digits — the number of digits in a sum is not fixed, you have to look at the actual numbers.