Question

A bag contains 5 black and 3 red balls. A ball is taken out of the bag and is not returned to it. If this process is repeated three times, then what is the probability of drawing a black ball in the next draw of a ball? (a) 0.7 (b) 0.625 (c) 0.1 (d) none of these

Answer 1

Answer:

Probability of 4th ball being black when

All first first 3 draws are black balls =58×47×36×25=1201680

First three draws contain all red balls =38×27×16×55=301680

First three draws contain 2 red and 1 black ball =38×27×56×45×3=3601680

First three draws contain 1 red and 2 black ball =38×57×46×35×3=5401680

Summing all above probabilities gives =58=0.625