A movie star, unwilling to give his age, posed the following riddle to a gossip columnist: "6 years ago, I was 13 times as old as my daughter. Now I am 7 times as old as she is." How old is the movie star?

To answer this question, you need to turn the description into an equation. If F is the father and D is the daughter, the equation would be:

1. (F-6) = 13 (D-6)

F-6 = 13D - 78

2. F = 7D

D = 1/7F

If you put the 2nd equation into the 1st equation, you can determine the movie star (father) ages. The calculation would become:

F-6 = 13 (1/7F) - 78

F-6 + 78=13/7 F

13/7F - F = 72

6/7F = 72

F = 72 * (7/6) = 84 years