posted by Bob .
Bob is at an amusement park with 10 different rides. He only has time to go on 3 rides, before he needs to head back for his curfew. If he only wants to go on each ride a maximum of one time, how many different ways are there to go on 3 rides?
he has 10 choices for the first ride.
Having ridden that one, there are only 9 choices for the 2nd ride, and so on.
Taking 3 rides, he has 10*9*8 = 720 ways to pick 'em.