13. The combined ages of Mark and Andrew are 44, and Mark is twice as old as Andrew was when Mark was half as old as Andrew will be when Andrew is three times as old as Mark was when Mark was three times as old as Andrew. How old is Mark? If you cannot work it out, ask your friends to help you, and watch the bewilderment creep over their faces as they attempt to grapple with the problem.
15. Mrs. Murphy wanted some oranges, so she sent Margaret to the corner shop to get them. Margaret came back a few minutes later with some oranges and six lollipops, having spent a total of 43 cents. Unfortunately, she didn't buy enough oranges, so her brother Mike was sent to get some more. He returned soon after, also with some oranges and seven sticks of toffee, having spent the same amount as his sister. What are the prices of the oranges, the lollipops, and the toffee sticks? Each of the items costs a whole number of cents, and all the items are realistically priced.
19. Molly is buying some new fishing equipment at a sporting goods store where there is a sale. Everything in the store is 25% off, and cash purchases receive another 25% off the sale price. What will Molly pay in cash for fishing equipment with a pre-sale price of $100?