Past experience has shown that the standard deviation of the weights of the bubble gum balls produced by a certain machine is 0.5 grams. If 90% of the population weigh more than 8 grams each, what is the mean of the population, assuming that the weights are approximately normally distributed? Class Limits Frequency 14-16 4 17-19 20-22 16 23-25 23 26-28 17 29-31 8 32-34 3