Question

A bin has 5 white balls and k black balls in it, where k is an unknown positive integer. A ball is drawn at random from the bin. If a white ball is drawn, the player wins 1 dollar, but if a black ball is drawn, the player loses 1 dollar. If the expected loss for playing the game is 50 cents, then what is k?

Answer 1

Step-by-step explanation: The expected loss is 50 cents, we know that it is more likely to lose than win. It is therefore difficult to get-50, so the overall difference between the two possibilities is 2, 50/200=1/4, and the probability to win is 1/4, and the probability to lose is 3/4. Since (1/4)*3=3/4, the number of black balls is 3 times the number of white balls, so k=15.