Mindbender: Sandtimers

You have two traditional hourglass type egg timers. One takes seven minutes for the sand to run through, the other takes 11 minutes. You want to boil an ostrich egg for exactly 15 minutes. How do you do it? and how soon after the start of the whole process will the egg be ready?

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ANSWER

Start both timers together. When the 7 minute timer finishes, turn it over immediately. It will run for 4 minutes before the 11 minute timer finishes. Turn the 7 minute timer over again at that point and it will measure a further 4 minutes : 15 minutes in total.

Alternative

"assuming that the water is already boiling start by turning over both timers when the 7min timer runs out drop the egg in the water there will be 4 min left on the 11 min timer when the 11min timer runs out flip it for the remaining 11 min (11min+4min=15min) add the 7 min from the original timer you get 22min (or since you used the 11min timer twice)"

Submitted by Linda Ostlie

 

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