Question

A box contains 3 blue and 2 red pens while another box contains 2 blue and 5 red pens. a pen drawn at random from one of the boxes turns out to be blue. what is the probability that it came from the first box

Answer 1

There are 5 blue pens total, 3 are from the first box and 2 are from the second. The probability of pulling a blue pen from the first box and not the second is 3/5.