Question

A box contains 10 red marbles, 20 blue marbles and 30 green marbles. 5 marbles are drawn from the box, what is the probability that ) atleast one will be green?

Answer 1

P(atleast one will be green)

= 1 -P(none of marbles are green)

first calculate probably that none of marbles are green

let B be the event that none of marbles are green

if the marble is not green, it will be red or blue

hence out of 30 marble 5 are selected

hence n(B) = 30C5

P(B) = n(B) / n(S)

     = 30C5/60C5

P(atleast one will be green) = 1 - P(none of marbles are green)

                 = 1 - 30C5/60C5