TT1-36

诡异儿

Each signal that a certain ship can make is comprised of 3 different flags hanging vertically in a particular order.  How many unique signals can be made by using 4 different flags?

 

A.      10

B.      12

C.      20

D.     24

E.      36

我选12,答案24. 牛人指导一下.

feierer

要考虑不同的排列顺序，所以是A(3,4)=24

ououbodao

A（3，4）是什么概念呀？

MerisaLees

It's a permutation case:

nPr = n!/(n-r)!

We need to choose 3 flags from the available 4 and arrangement in a specific order matters. So, it's 4p3 = 4! = 24 signals

So, the answer is (D)

诡异儿

多谢啦!