1. ## Hourglass Figure

You have a 4 minute and a 7 minute hourglass. How do you measure 9 minutes?

2. ## Re: Hourglass Figure

<span style="background-color: #FFFF00; color: #000000; font-weight: bold"><font color=yellow>Start both hourglasses at the same time. Each time one of them runs down, turn it around immediately.
The 9 minute period starts when you turn around the 4 minute hourglass for the 3rd time (i.e. after 12 minutes) and ends when you turn around the 7 minute hourglass for the 3rd time (i.e. after 21 minutes)</font color=yellow></span hi>

3. ## Re: Hourglass Figure

Oh oh!! I gotta try this one!! <span style="background-color: #FFFF00; color: #000000; font-weight: bold"><font color=yellow>I would start the 7 minute hour glass. When it is empty, don't restart it but immediately start the 4 minute glass and let it run until it is half empty! </font color=yellow></span hi> <img src=/S/grin.gif border=0 alt=grin width=15 height=15>

4. ## Re: Hourglass Figure

<span style="background-color: #FFFF00; color: #000000; font-weight: bold"><font color=yellow>Even if I had those "hour" (sounds like a misnomer to me) glasses, I would tend to use my trusty stopwatch. It gets much better precision and is more general.</font color=yellow></span hi>

Steve

5. ## Re: Hourglass Figure

That would work, but my solution takes 9 minutes from the first turn.

6. ## Re: Hourglass Figure

Or until it's only half-full! <img src=/S/devil.gif border=0 alt=devil width=15 height=15>

7. ## Re: Hourglass Figure

See the world in a grain of sand - and so many of them! <img src=/S/dizzy.gif border=0 alt=dizzy width=15 height=15>

8. ## Re: Hourglass Figure

<span style="background-color: #FFFF00; color: #000000; font-weight: bold"><font color=yellow>Start 4 & 7 minute hourglasses together.
When 4 minute hourglass drains turn it over (4 minutes elapsed)
When 7 minute hourglass drains turn it over (7 minutes elapsed)
When 4 minute hourglass drains for 2nd time turn over 7 minute hourglass (8 minutes elapsed)
The 7 minute hourglass will drain again in a further minute, total time elapsed is 9 minutes.</font color=yellow></span hi>

9. ## Re: Hourglass Figure

Fools seldom differ!

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