Mother makes tasty toast in a small pan. After toasting one side of a slice, she turns it over. Each side takes 30 seconds. The pan can only hold two slices.
How can she toast both sides of three slices in 1 & 1/2 instead of 2 minutes?

toasts A, B, C (sides 1 and 2)
0-0.5 min ... A1 B1
0.5-1 min ... A2 C1
1-1.5 min ... B2 C2