試題詳解

76. There are 5 ways to write 4 as a sum of positive numbers, namely 5, 4+1, 3+2, 2+1+1, 1+1+1+1+1. Note that the order of the summands is irrelevant. How many ways are there to write 8 into a sum of positive numbers, with order or the summands irrelevant?
(A) 20
(B) 21
(C) 22
(D) 23