Question 248725
nCr=n!/((n-r)!r!)
There are 10 socks.
.
Pick a gray pair:
2C2 / 10C2 = 1/45
.
4C2 / 10C2 = 6/45 blue pair or black pair
.
Any pair: 6/45 + 6/45 + 1/45
=13/45
.
Ed