[Guest]

Your grandfather is staying at your house. One day he gets sick and tells you "I need an egg, newly cooked for exactly 15 minutes in 15 minutes or I will faint". A problem you encounter is that the only timing devices you have are a 7 minute hourglass and an 11 minute hourglass. How will you do it?

[bonanova]

Set both timers running.

After 7 minutes invert the 7-minute timer.

At 11 minutes, turn 7-minute timer again.

When it runs out your egg is done.

[rookie1ja]

good one, however, it's already posted - check Sand-glass II.

there is more of this type in the section called Water and Weighing Puzzles

looking forward to new puzzles ... this thread is locked