Answer:

There are 15,120 ways to arrange 3 red, 2 yellow, and 2 blue builds in a string of Christmas tree lights with 9 sockets.

Solution:

P = 9! / 3! • 2! • 2!

P = 9•8•7•6•5•4•3•2•1 / 3•2•1•2•1•2•1

P = 9•8•7•6•5•4•3•2•1 / 6•4 ( eliminate 6 and 4)

P = 9•8•7•5•3•2•1

P = 15,120

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Answer:

We have "9 sockets choose 3" for the 3 red lights. That's (9C3) ways.