1. a class enters a competition to design a new flag. there are given a choice of five colours: blue, red, green, orange and yellow. the flag must have three bands of colour, but the colours can be in any order. how many different flags can be class design?
2. How many ways are there of colouring in 3 sections, using 3 out of 4 colours, if order of the colours in not important?
这两道题是排列还是组合？
评论
题目很简单，但楼主英文欠佳，理解不了这两句话。
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