You are taking out candies one by one from a jar that has 10 red candies, 20 blue candies, and 30 green candies in it. What is the probability that there are at least 1 blue candy and 1 green candy left in the jar when you have taken out all the red candies? (Candies of same color are indistinguishable!) Hint
Combinatorial problem. Consider a sequence of 60 candies, in which red candies finish before blue and green.
It can be done using combinatorics as well as conditional probability. I don't have time today, but please remind me to put proper solution by commenting down below or by sending me a message. Thank you.