17. Veronica put on five rings: one on her little finger, one on her middle finger and three on her ring finger. In how many different orders can she take them all off one by one?
A 16
B 20
C 24
D 30
E 45
SolUtion
B

There are five options for when the ring on the little finger is removed. There are then four options for when the ring on the middle finger is removed. There are then no options for when the three rings on the ring finger are removed since they must be taken off in order in the three remaining slots. So there are $5 \times 4=20$ possible orders.