A bag contains 5 red, 6 where and 7 black balls. Two balls are drawn at random. what is the probability that both balls are red or both are black?

Explanation

Step 1: Case 1- Both red

Total number of balls `=18`

Probability `=5/(18)​xx4/(17)​`

Step 2: Case 2-Both black

Probability `=7/(18)​xx6/(17)`

Step 3: Total probability

Total probability `=(5xx4)/(18xx17)​+(7xx6)/(18xx17)​ `

=Total probability `=(31)/(153)`