math

posted by ana

a draw holds 5 navy socks, 7 white socks and 6 black socks. if two socks are selected at random without looking what is the probability that they do no match?

1. MathMate

Ways to get 2 socks out of 18
=(18,2)=18!/(2!(18-2)!)
=153
Ways to get 2 navy socks
=(5,2)
Ways to get 2 white socks
=(7,2)
Ways to get 2 black socks
=(6,2)
So ways to get two different coloured socks
=(153-(5,2)-(6,2)-7,2))
out of a total possible 153 ways.

Calculate the probability.
I get less than 70%.

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