How many ways can you make 123 with subtracting 3 digit numbers?

Answer 1

900 or 1,800, depending upon the domain restriction.

Subtracting natural numbers or whole numbers only, you simply subtract x from 123 + x where x is greater than or equal to 100 (the lowest three digit whole number) and less than or equal to 999 (the greatest 3 digit whole number).

The equation is as follows:

123 = (x +123) - x

However, if the domain is all integers, the answer doubles to include the opposites of the aforementioned set of numbers, or -999 to -100. The above equation also describes this situation.