Question

A box contains 12 black and 8 green marbles. How many ways can 3 black and 2 green marbles be chosen?​

Answer 1

Answer:

The simplest solution is to calculate the probability none of the 3 is red, then subtracting that number from 1 gives the answer.

The number of possible triplets = 20!/(17! 3!)=20*19*18/6=1140

The number of non red cases = 8!/(5! 3!) = 8*7*6/6=56

The probability at least 1 is red = 1 -56/1140 =.9508