Ok It depends upon what the order of the terms might be
If we consider that the positive mixed number is the first term and the negative mixed number is the second term and we consider "difference" to be subtraction.....then the result is positive
For example
(3 + 1/2) - [ -(1 + 1/2)] =
(3 +1/2) + (1 + 1/2) = 5 since subtracting a negative results in a positve
But....if we had the reverse order with the same operation, we would have
-(1 + 1/2) - (3 + 1/2) and the result is - 5
Hence.......I would go with "sometimes"