1.There are 20 multiple choice questions in an examination paper. To prevent students from guessing at answers, the teacher decided to deduct x marks for each wrong answer and give 5 marks for each correct answer . Assume that each question has 5 options.
(a) If the teacher intends to set zero mark for the paper by pure guesswork , find the value of x.
probability about maths
2008-01-29 5:09 am
回答 (2)
2008-01-29 5:24 am
✔ 最佳答案
1(a)The probability to guess the correct answer=0.2
The probability to guess the wrong answer=0.8
Expected value=0.2*5+0.8(-x)=1-0.8x
If the teacher intends to set zero mark for the paper by pure guesswork , then expected value=0
So 1-0.8x=0
x=10/8=5/4
2008-01-29 7:05 am
一個亂撞既學生，有五份一機會答對一題
現在一份卷有廿題，咁佢平均可以撞對四(20除5)題，撞錯十六題。
撞對的有20分，如果個數學阿sir想底銷呢個『符碌』分數，
咁嗰16個錯答案就應該倒扣番20分至啱，即係每個錯需要倒扣20/16分(即係 1.25分) lor...
現在一份卷有廿題，咁佢平均可以撞對四(20除5)題，撞錯十六題。
撞對的有20分，如果個數學阿sir想底銷呢個『符碌』分數，
咁嗰16個錯答案就應該倒扣番20分至啱，即係每個錯需要倒扣20/16分(即係 1.25分) lor...
收錄日期: 2021-04-26 13:44:18
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080128000051KK03172