we are picking the four balls without replacement and that the 4 white and 4 red balls are the only balls in the box and that we choose 2 red balls and 2 white balls. Number of ways to choose 4 balls out of 8=8C4=
8!
4!4!
=70 Number of ways to pick 2 red balls out of 4=4C2=
4!
2!2!
=6 Number of ways to pick 2 white balls out of 4=4C2=