An urn contains 9 red, 7 white and 4 black balls. If two balls are drawn at random, find the probability that: (i) both the balls are red,(ii) one ball is white (iii) the balls are of the same colour (iv) one is white and other red.

Explanation

`n(S)=.^20C_2`

`P_1=(.^9C_2)/(.^20C_2)`

`P_2=(.^7C_1*.^13C_1)/(.^20C_2)`

`P_3=(.^9C_2+.^7C_2+.^4C_2)/(.^20C_2)`

`P_4=(.^9C_1*.^7C_1)/(.^20C_2)`.