Question

一道概率题目

设随机变量X的概率分布为（P=K）=a除以5的K次方，a为常数，k=1,2……，则a=？

Answer 1

(P=1) = a/5
(P=2) = a/5^2
...
(P=K) = a/5^k
等比数列求和，得S=a/4 = 1
a = 4