math
posted by tg .
a box filled with identically shaped balls contains 5 balls with the number 1 on them, 8 balls with the numbers 10 on them, 15 balls with the number 12, and 2 balls with the number 20 on them. If the balls cannot be seen from outside the box, and if one ball is picked at random from the bag, what is the probability that it has the number 12?

P(12) = 15/(5+8+15+2) = ?