In Quiz Master Shop Towers we have a grill which we use to make toast. We can fit three slices of bread under the grill, and it takes one minute to toast one side of the bread.
How can we make four pieces of toast, all toasted on both sides, in three minutes?
Place three pieces of bread under the grill and toast for one minute,
Turn over two of the three pieces of bread and replace the other piece of bread with the fourth piece of bread and toast for one minute,
Remove the two pieces of bread that are toasted on both sides, turn over the other piece of bread and return the other piece of bread to be toasted for one minute.
If A, B, C and D are the four pieces of bread and 1 and 2 are the two sides, for each of the three minutes you toast:
A1 B1 C1
A2 B2 D1
C2 D2