In how many ways can 27 be written as the sum of two positive integers? (Ignore the order of the numbers.)
In some places 0 is considered positive and negative, some neither.
I'll go with the assumption 0 is neither since where I live that's the definition.
Thus we have the pairs...
1 through 26 is 26, so we have 26 pairs. There are 13 distinct pairs and times 2 for the ability to flip over. This is because 27 is odd and 27/2 isn't an integer.
If the number was odd however we would have a pair (even num.)/2 and we can't flip that.
If you don't understand anything feel free to ask!
(sorry for the late answer!)