Question

There are 60 balls, 17 are red and the rest are black. If I draw 7 balls what's the probability that at least 3 are red?

Answer 1

prob(red) = 17/60
prob(not red) = 43/60

have to exclude zero red, one red, and two red
prob zero of 7 red
= C(7,0) (17/60)^0 (43/60)^7
= appr .0971

prob one of 7 red
= C(7,1) (17/60) (43/60)^6
= appr .2687

prob two of 7 red
= C(7,2) (17/60)^2 (43/60)^5
= .3187


prob of getting at least 3 of 7 red
= 1 - .0971 - .2687 - .3187
= appr .31547

check my arithmetic