Sands of Time

You have two old-fashioned sand-glass timers; one takes seven minutes for the sand to filter through and the other takes eleven minutes.

The problem is to find the most efficient way of using the two sand-glasses to time the cooking of a 15-minute hard-boiled egg. Starting from the instant the first sand-glass timer is upturned, what is the minimum overall time in which cooking can be accomplished?

-Ray.

At first glance it can be done by starting both at the same time, after the 7min sandtimer is empty you start cooking the egg. At this point there is 4min left in the 11min sandtimer, so you run the 4min then use the full 11min timer again. Total time 22min.

Sure it can be done quicker though if I had more time to think..... back to work.

Originally posted by rgoudie
You have two old-fashioned sand-glass timers; one takes seven minutes for the sand to filter through and the other takes eleven minutes.

The problem is to find the most efficient way of using the two sand-glasses to time the cooking of a 15-minute hard-boiled egg. Starting from the instant the first sand-glass timer is upturned, what is the minimum overall time in which cooking can be accomplished?

-Ray.

15 mins
put the egg in and turn both timers
after 7 mins timer7=0, timer11 = 4, turn timer 7
after 7+4 minutes timer7=3, timer11=0, turn timer 7(now it has 4 left)
after 7+4+4 minutes timer7 =0

Originally posted by iamatiger
15 mins
put the egg in and turn both timers
after 7 mins timer7=0, timer11 = 4, turn timer 7
after 7+4 minutes timer7=3, timer11=0, turn timer 7(now it has 4 left)
after 7+4+4 minutes timer7 =0

Go Freethinkers! 😀

Originally posted by iamatiger
15 mins
put the egg in and turn both timers
after 7 mins timer7=0, timer11 = 4, turn timer 7
after 7+4 minutes timer7=3, timer11=0, turn timer 7(now it has 4 left)
after 7+4+4 minutes timer7 =0

Correctamundo!

-Ray.

I reckon the most efficient way would be to not be such a tight git and go out and buy a 15 minute timer.