5954概率中等数值题medium

Just These Two

题目

Coupons arrive uniformly and independently from 5 types. You only care about two SPECIFIC types, the gold and the silver coupon; the other three are worthless to you. What is the expected number of draws until you have collected BOTH the gold and the silver coupon?

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你的答案

数值

draws

只填写数值本身，单位 draws 已固定在输入框右侧。