If he only has a three-minute timer (hourglass), and a five-minute timer can he boil the egg for only two minutes?
See the answer
Once the water is boiling, Dr. Johnson needs to turn the three-minute timer and five-minute timer over. When the three-minute timer runs out, he needs to put the egg in the boiling water. When the five-minute timer runs out, two minutes have elapsed and it is time to take the egg out of the water.