Question

A bag contains 4 white and 5 red marbles. Two marbles are drawn one after the 1 other without changing. Find the probability of getting both as white marbles.

Answer 1

n = (4W + 5 R) = 9 ways to draw one ball from 9 balls

Let probability of drawing white and red marbles be P(W) and P(R)

P(drawing 2 white marbles one after the other)

= P (2W) = P 

(white marble in I draw) and P (drawing white marble in II draw)

P(WI ∩ WII) = P (WI) P (WII/ WI)

P(A ∩ B) = P(A) P(B/A)

= 4/9 x 3/8 = 12/72 = 1/6

Here, first drawn ball is not replaced.