There is a bag with only red marbles and blue marbles. The probability of randomly choosing a red marble is 7 8 . There are 72 marbles in total in the bag and each is equally likely to be chosen. Work out how many red marbles there must be.

The salesperson earns a 5% commission on the first $5,000 she has in sales. the salesperson earns a 7.5% commission on the amount of her sales that are greater than $5,000. this month the sales person had $8,000 in sales. what amount of commission, in dollars, did she earn?