Thread: probability of picking a ball (this is easy :P)

if there are n balls in a bag, 1 black and n-1 white, and i take k balls out of the bag, how come the probability of taking a black is k/n?

I get that it works if you try adding the probabilities of getting black on the 1st, 2nd..kth attempt, but whats the logic behind it?

Just do the caculation:

thanks, why is that the calculation?

Originally Posted by Aquafina

thanks, why is that the calculation?

Well you choose one black ball from 1 and k-1 white balls from n-1 white balls.