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题库 / OG2017Q-PS-158
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?
20
25
40
60
125
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C51*C41=C53*C21=A52
A55/A33
identical 完全相同的 5!/3！
5辆车中选择了两辆出来之后，剩下的就自动填上去了，没得选择了，因为剩下的3辆是一模一样的，不需要有顺序。P(5，2)=20或者C5(3)*C2(1)=20
5!/3! =20
C(5,3)*C(2,1)=20