Expected score

northwolves · 发表于 2011-1-17 20:54:03

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http://projecteureka.org/problem/question/1183

Expected score
Jeo has a 50 point quiz at 11 am. He wakes up at a random time between 10 am and noon, then arrives at class 15 minutes later. If he arrives on time, he will get a perfect score, but if he arrives more than 30 minutes after the quiz starts, he will get a 0, but otherwise, he loses a point for each minute he's late (he can lose parts of one point if he arrives a nonintegral number of minutes late). What is Jeo's expected score on the quiz?

Solution Format/Example: rational number x/y, where gcd (x, y) = 1

wayne · 发表于 2011-1-17 21:54:07

本帖最后由 wayne 于 2011-1-17 22:09 编辑

55/2

wayne · 发表于 2011-1-17 22:10:51

晕,刚才太粗心
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这题其实很简单

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