The Pit and the Pendulum
The Answer: The rat should chew through the rope 45 seconds before the pendulum blade reaches your chest.
1. You know that the rat will take 1 minute (60 seconds) to chew through the rope.
2. The pendulum blade is 15 inches above your chest and it lowers 1 inch with each swing. How many swings will it take the blade to reach you? Divide the height the blade is above you (15 inches) by the number of inches it drops per swing (1 inch). 15 swings