5 students are selected from the top 10 students of a class. Find the number of all possible combinations in which the student ranked sixth in class is the third best among the selected students.
ans. is 60.
please explain and shows the steps.
thx~~
f5~permutation and combination
2012-01-09 2:12 am
回答 (1)
2012-01-09 2:24 am
✔ 最佳答案
Step 1 :Choose 2 students among the top 5 , 5C2 ways.Step 2 :
Choose the student ranked sixth , 1 ways.Step 3 :
Choose 2 students among ranked 7th to 10th , 4C2 ways.Ans :5C2 * 1 * 4C2 = 10 * 1 * 6 = 60 ways.
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