PUMaC 2012 · 组合（B 组） · 第 1 题
PUMaC 2012 — Combinatorics (Division B) — Problem 1
题目详情
- [ 3 ] Your friend sitting to your left (or right?) is unable to solve any of the eight problems on his or her Combinatorics B test, and decides to guess random answers to each of them. To your astonishment, your friend manages to get two of the answers correct. Assuming your friend has equal probability of guessing each of the questions correctly, what is the average possible value of your friend’s score? Recall that each question is worth the point value shown at the beginning of each question.
解析
- By linearity of expectation, the answer is 2 × = 10 . 8