Question

There is a bag filled with 3 blue, 4 red and 5 green marbles.

A marble is taken at random from the bag, the colour is noted and then it is
not replaced.
Another marble is taken at random.
What is the probability of getting 2 reds?

Answer 1

Total marbles to start = 3 + 4 + 5 = 12

the probability of getting red is the number of red / total marbles.

first pick getting red = 4/12 = 1/3

after the first pick there would be 3 red and 11 marbles. The probability of picking red would be 3/11

the probability of picking red twice would be 1/3 x 3/11 = 3/33 = 1/11

Answer: 1/11