One ordering of the leters T,U,V and W from left to right is UTVW.What is the totaal number of order

题目

One ordering of the leters T,U,V and W from left to right is UTVW.What is the totaal number of ordering of these letters from left to right,including UTVW?

答案

一共有：4*3*2*1 = 24种排序.
左边第一个字母有4种选法（T, U, V, W 4个字母选一个）,然后第二个字母有3种选法（此时只有3个字母可选）,然后第3个字母有2种选法,最后只有一个字母,所以共有 24 种排序.
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