MATHS QUESTION

hihi

2007-04-25 3:47 am

There are 4 MC questions in a short quiz and 5 options are given to each question. Two marks are awarded for a correct answer and one mark is deducted for a wrong answer. No marls will be awarded or deducted for unattemption questions.

Find the number of ways to get a total score of 2 marks.

回答 (1)

Bon

2007-04-25 5:15 am

✔ 最佳答案

Possible choices of correct answer: 0,1,2,3,4

0 is impossible because the total score <= 0
3 is impossible because the total score >=3*2-1 = 5
4 is impossible because the total score = 8

In order to get 2 marks with 1 correct answer, one must leave the rest of the questions blank. So # of ways to have 1 correct answer, and the rest blank, is 1 choose 4 = 4.

In order to get 2 marks with 2 correct answer2, one must answer the rest of the questions incorrectly. So # of ways to have 2 correct answer, and the rest wrong, is 2 choose 4 = 6.

Therefore, total number of ways = 4+6 = 10.

參考: don't delete the question this time.

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