What is the answer?

Question

A bag contain 3 black discs and 7 white discs.A disc is taken at random from the bag and not replaced.This is carried out three times.Calculate the probability of getting a black disc followed by two white discs.

Answer 1

There are 10 discs initially, and the probability of drawing a black disc first is 3/10, leaving 9 discs, 7 of which are white. Probability of drawing a white disc next is 7/9, leaving 8 discs, 6 of which are white. Probability of drawing another white disc is 6/8.

Multiplying the probabilities we get: 3/10*7/9*6/8=7/40=0.175.