Question

A bag contains 4 white and 2 black balls.
4 balls are successively drawn out
without replacement. What is the
probability that they are alternatively of
different colour?

● 2/15
● 1/5
● 2/9
● 1/6​

Answer 1

Given :

- A bag contains 4 white and 2 black balls.

- 4 balls are successively drawn out

without replacement

To find :

The probability that they are alternatively of different colour

Solution :

There are two cases,

1) black + white + black + white

2) white + black + white + black

For first case,

Probability, P = 4/6 + 2/5 + 3/4 + 1/3

P = 1/15

For second case,

Probability, M = 2/6 + 4/5 + 1/4 + 3/3

M = 1/15

Total probability, T = P + M

T = 1/15 + 1/15

T = 2/15