With a seven-minute sand timer and an eleven-minute sand timer describe a method to time the boiling of an egg for 15 minutes?

Answer 1

start the both of them at the same time, when 3 mins is up there is 4 mins left on the 7 minute timer. so reset the timer and start again. when that finishes that is 11 mins

Answer 2

First Answer: Start the 7 and 11 minute timers at the same time. When the seven minute timer runs out put the egg in. When the 11 minute timer runs out, start it again. When that runs out, the egg has been cooking for fifteen minutes.

Improved Answer: It would be faster to start the egg and both timers. When the 7 runs out, start it again. When the 11 runs out, flip the 7 over. The four minutes that went down in the 7 will now be on top. When it runs out, the egg will have been in for 15 minutes.

Answer 3

Flip both hour glasses at the same time. When the 7 minute one is finished, you should have four minutes left on the 11 minute hour glass and one finished 7 minute hour glass. You have now been boiling for seven minutes.

Then, immediately flip the 7 minute hour glass over again, but leave the 11 minute hour glass the way that it was. It will continue to count down for the last 4 minutes. You now have been boiling for 11 minutes, have one finished 11 minute hour glass and 3 minutes remaining in the 7 minute hour glass. As soon as the 11 minute hour glass finishes, flip the 7 minute hour glass back over, even though it has not finished draining, because there is now 4 minutes on the other side of the 7 minute hour glass. Once that hour glass finishes draining, it will have been 15 minutes.