Question

How many ways can you add 3 non-negative integers so the sum is less than 10?

Answer 1

0+1+9, 0+2+8, 0+3+7, 0+4+6, 0+5+5 gives 27 ways including permutations.
1+1+8, 1+2+7, 1+3+6, 1+4+5 gives 21 ways.
2+2+6, 2+3+5, 2+4+4 gives 12 ways
3+3+4 gives 3 ways
With permutations this gives 27+21+12+3=63 ways.