# Uneven hourglass

Using only a four-minute and a seven- minute hourglass, measure exactly nine minutes?

It is possible to use multiple hourglasses

Note by Beakal Tiliksew
4 years, 3 months ago

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start 4 and seven together after 4 min 4minhourglass would e empty and 7 minhrglass would have 3 min left , flip 4 in hr glass after 3 min 7min hr glass would empty ,so flip it and after 1 min 4 hrmin glass woul be empty and 7 hrmin glass have 6 min left so flip it and after and wait for 7 min hrglass to empty now nine mins have been calculated

- 4 years, 3 months ago

Think about this: 44 - 17 == 9. Let us denote the four-minute hourglass by A, the seven-minute one by B. Take 2 A's and 1 B. Use the two A's consecutively and a B in parallel so that upon the completion of the B the two A's contain 1 minute each. Then launch the two A's in succession to measure the remaining 2 minutes.

- 1 year ago

Start and stop when any of the glass is empty and calculate time 4 Min>>>0 Min and 7 min>>>0 Min 0 Min>>>4 Min and 3 Min>>>4 Min ------4Min Flip 4 min Hourglass and Continue 7Min Hourglass
3 Min<<<1 Min and 0 Min>>>7 Min ------7Min Continue 4 Min Hourglass and Flip 7Min Hourglass 4 Min<<<0 Min and 1 Min<<<6 Min ------8Min Flip both Now 3 Min>>>1 Min and 0 Min >>>7 Min ------9Min

- 4 years, 3 months ago