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%.