We have a box with eight green marbles five red marbles and

We have a box with eight green marbles, five red marbles, and seven blue marbles. We choose three marbles from the box at random without looking. Write the probability in decimal form rounded to three places. What is the probability that they will all be blue?

Solution

Total marbles 8+5+7=20

Choosing 3 marbles is 20C3=1140

Choosing 3 blue marbles is 7C3=35

Probability is 35/1140=0.0307