self Maths Puzzle

in a bag there are 10 black,8 white,and 5 red balls.three balla are chosen at random and one is found to be black.the probability the the rest two are white is?

Read Solution (Total 2)

since 1 ball drawn is black remove that from total.. then find probability of selecting 2 whites from them
8c2/22c2=(8*7/2)/(22*21/2)=4/33
11 years agoHelpfull: Yes(6) No(0)

8/22*7/21=4/33
11 years agoHelpfull: Yes(3) No(0)

self Other Question

counters marked 1,2,3 are placed in a bag and one of them is withdrawn and replaced.the operation being repeated three times,what is the chance of obtaining a total of 6 in these three operations. the probability of a bomb hitting a bridge is 1/2 and twodirect hits are neede to destroy it.the least no of bombs required so that the probability of the bridge being destroyed is greater than 0.9 is?