-2

这是任务

How many ways are there to choose from the set {1, 2, . . . , 100} three distinct
numbers so that their sum is even?

首先，三个数字的总和是即使只有

1.all number is even
2.two of them is odd and one is even

我知道 

(n)   =  n!/(k!*(n-k)!   
(k)

谁能帮我解决这个问题

4

1 回答 1

1

那岂不是很简单

(50 choose 3) + (50 choose 2) * (50 choose 1)

?

于 2010-06-13T07:36:30.117 回答