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#### Alexmahone

##### Active member

- Jan 26, 2012

- 268

- Thread starter Alexmahone
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- Thread starter
- #1

- Jan 26, 2012

- 268

- Jan 26, 2012

- 890

Start then together, turn the 4 when it is emply. When the 7 is empty start timing the nine minutes, at this point the four minute glass has 1 minute to go. When empty turn it, 5 minutes have elapsed. Turn it again, and when empty 9 minutes have elapled.

CB

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- #3

- Jan 26, 2012

- 268

Now there are 3 minutes remaining in the 7.Start then together, turn the 4 when it is emply.

When the 7 is empty there is 1 minute remaining in the 4. So why would you want to turn it?When the 7 is empty turn the 4.

At this point it has 1 minute to go...

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- Jan 26, 2012

- 890

Typo, now corrected (I hope)Now there are 3 minutes remaining in the 7.

When the 7 is empty there is 1 minute remaining in the 4. So why would you want to turn it?

CB

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- Jan 26, 2012

- 268

Okay, that works but it's a little inefficient as it wastes the first 7 minutes. There's a better solution.Start then together, turn the 4 when it is emply. When the 7 is empty start timing the nine minutes, at this point the four minute glass has 1 minute to go. When empty turn it, 5 minutes have elapsed. Turn it again, and when empty 9 minutes have elapled.

CB

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- #6

- Jan 26, 2012

- 268

- Jan 26, 2012

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Start the two together. When the four is empty, flip it (four minutes elapsed). When the seven is empty, flip it (7 minutes). When the four is empty again flip the seven (8 minutes). Wait then the remaining minute for the seven to empty.

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yes +1Hint: There is a solution that wastes no time and measures 9 minutes in one go.