请教GWD30-31?

joezhouyun

Q31:

There are 5 cars to be displayed in 5 parking spaces with all the cars facing the same direction.  Of the 5 cars, 3 are red, 1 is blue, and 1 is yellow.  If the cars are identical except for color, how many different display arrangements of the 5 cars are possible?

 

 

A.    20

B.    25

C.    40

D.    60

E.    125

                                       Answer:

答案为Ａ，请问如何解答？

assurance

不用考虑红车，先从5个车位中选一个放蓝车，在从剩下4个车位中选一个放黄车，5×4＝20

joezhouyun

i see, thank  you !!!