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Measuring Problem

A teacher of mathematics used an unconventional method to measure a 15-minute time limit for a test. He just used 7 and 11-minutehourglasses. During the whole time he turned sandglasses only 3 times (turning both hourglasses at once count as one flip).
Explain how the teacher measured 15 minutes.

For Solution: Click Here

1 comment:

  1. A: 7 minutes hourglass
    B: 11 minutes hourglass

    1) Turn A & B.
    2) When A expires, turn A again (7 m so far)
    3) When B expires, turn A again(11 m so far)
    4) When A expires, we have 15 minutes from 1).