78:S = {1,3,5,7, …,397,399}Set S consists of the odd numbers from 1 to 399, inc

游客2024-01-12  13

问题 78:S = {1,3,5,7, …,397,399}
Set S consists of the odd numbers from 1 to 399, inclusive. How many different ordered points(p,t) can be formed, where p and t are numbers in S and p<t? (Note:The sum of the integers from 1 to n, inclusive, is given by the formula n(n+1)/2 for all positive integers n.)

选项 A、19,900
B、20,000
C、49,500
D、79,600
E、79,800

答案 A

解析 本题可使用枚举法答题。

199+198+197+…+1=199×(199+1)/2=19,900个可能的组合。故答案为A。
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