A box contains 10 red balls and 10 green balls. Five draws are made without replacement.

Find the probability of selecting 4 balls of the same colour.

1 answer

could be 4 green and one red , or, 4 red and 1 green
prob(the stated event) = ( C(10,4)*C(10,1) + C(10,4)*C(10,1) )/C(20,5)
= .....