For his breakfast, Mr. Stone likes an egg that has been boiled for exactly 9 minutes. He has two egg timers (those with sand in them), one that runs for 4 minutes and one that runs for 7 minutes. How can he use these timers to boil his egg?
Answer
Start both egg timers. When the 4-minute timer runs out, turn it over. When the 7-minute timer runs out, turn it over. When the 4-minute timer runs out again, the 7-minute timer has been running for 1 minute. Turn it over once again. When it stops, the egg is done.
