Question

an urn contain 81 marble each of which is white, black or green the probability of selecting a white marble at random from the urn is 1/ 3 and the probability of getting a black marble at random is 4/9 how many green Marbles does the urn contain

Answer 1

total probability = 1

prob. green = 1- (1/3+4/9)
= 1- 7/9
=2/9

no . of green marbles = 81×2/9
= 18

Answer 2

no of white marble=1/3*81=27
no of black marble=4/9*81=36
so no of green are total-(white +black)
=81-63=18