Quandaries and Queries


I'm a student.Can I ask you a question?You have two hourglasses-one measures 7 minutes and one measures 4 minutes.How can you time 9 minutes?



Start both timers at the same instant. When the 4 minute timer runs out start it again immediately. When the 7 minute timer runs out this is the start of the 9 minutes. Can you see how to tell when 9 minutes are up?



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