Question: how many combinations of 2 numbers are there?
Answer: [You don't want to include (40,20) and (20, 40).] So that means you need to know how many different permutations there are for each combination. If there are two numbers, there are two permutations per combination. Divide the possible permutations by number of permutations per combination: 2450 / 2 = 1225.