Question

A bag contains 13 white and 7 black balls. Two are drawn at random . What is the probability that they are of the same colour ? A. 41 190 B. 21 190 C. 59 190 D. 99 190 Select the correct answer from above options

Answer 1

Correct Answer - D No . Of ways of getting 2 white balls =13C2 No. of ways of getting of getting 2 black balls =7C2 probability of the getting 2 same colour ball = probability of 2 white balls or probability of 2 black balls Total number of balls drawn ⇒13C2+7C2 ) 20C2 ⇒ 13! 2!×11! + 7! 2!×5! 20! 18!×2! ⇒ 13×12×11! 2!×11! + 7×6×5! 2!×5! 20×19×18! 18!×2! = 13×12+7×6 20×19 ⇒ 198 380 = 99 190