if mn=361,m and n being natural numbers ,which of the following could be a value of (m-n)/2?

Question

9.5,180,-8.5,none of these

Answer 1

Divisors of 361 are 1, 19, 361
361 = 1 × 361 or 19 × 19
m = 361 & n = 1 or m = 19 & n = 19
m – n = 360 or m – n = 0
360/2 = 180 or 0/2 = 0

Answer 2

I tried a while at this. But 361 doesn't appear to be divisible by any other number other than itself and 1. So if m is 1, n must be 360. Or vice versa. Thereby (m-n)/2 is either (361-1)/2 = 180 or (1-361)/2 = -180. So 180 could be a value of (m-n)/2.

Answer 3

The answer above is correct in that 180 is the answer.

But there is a slight mistake in his answer in that 361 is not a prime number - it happens to be 19 squared. However, 19-19/2 = 0, which isn't an option, so m and n must be 361 and 1 as he said.