An urn contains 5 green and 25 blue balls Balls are drawn at

An urn contains 5 green and 25 blue balls. Balls are drawn at random, one at a time, untill a green ball is selected. each ball is replaced before the next ball is drawn.

(a) what is the probability that at least 20 draws are needed?

Solution

Probability of drawing a green ball = 5/30 = 1/6

Probability of drawing a blue ball = 25/30 = 5/6

(a)

Probability that at least 20 draws are needed

= (5/6)^19 * (1/6)

= 0.0052 Answer