nPr and nCr 3(5m)

👨🏻‍🏫 學術台數學

用戶90882

2010-08-07 8:00 am

Using knowledge of nPr and nCr ,

How many diagonals are there in an octagon? Solutions: 20

I need steps. thank you. 5 marks

更新1:

2. There are 8 outstanding students from junior forms and 9 outstanding students from senior forms in a school this year. 5 out of these 17 students are now selected for an overseas exchange programme.

更新2:

Find number of combinations if selecting at least 1 student from junior forms and 1 from senior forms. Solutions: 6 006

回答 (1)

用戶2053

2010-08-07 8:15 am

✔ 最佳答案

Any two vertices confirm one diagonal or side ,So there are 8C2 = 28 diagonals or sides ,since an octagon have 8 sides ,so 28 - 8 = 20 diagonals are there in an octagon.

2010-08-07 00:38:40 補充：
2.

17C5 - 8C5 - 9C5 = 6006

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