Post Christmas hangover mind boggler!

[MonacoMike]

The first correct answer is the winner and winner gets the satisfaction of being first.

Measure exactly nine minutes, using only a seven-minute hourglass and a four-minute hourglass, without the process taking longer than nine minutes. Both hourglasses must be empty at the finish.

 

[Four Suns]

Start the 7 minute and 4 minute hour glass at the same time. When the 4 minute one runs out, flip them both... there is 3 minutes of sand in the 7 minute hour glass.

When the 3 minutes is up on the 7 minute one (it runs out), flip them both (there is 1 minute in the 4 minute hour glass)

When the 1 minute is up on the 4 minute one... flip them both... there is one minute in the 7 hour glass... when it runs out, you are at 9 minutes.

This, of course, assumes the sand falling out is linear with time... I'm not sure it is.

The "Democrat" answer is to say it's not fair that the 7 minute glass has more sand.... So you break the hour glasses and divide the sand equally... and you have more than 9 minutes and everyone wins.

 

[HUMPH]

Too much to think about but there are a bunch of flips going on.

Turn both over then when the 4M timer is empty, flip the 7M timer over leaving 3 minutes and so on, and so on...

 

[MonacoMike]

Start the 7 minute and 4 minute hour glass at the same time. When the 4 minute one runs out, flip them both... there is 3 minutes of sand in the 7 minute hour glass.

When the 3 minutes is up on the 7 minute one (it runs out), flip them both (there is 1 minute in the 4 minute hour glass)

When the 1 minute is up on the 4 minute one... flip them both... there is one minute in the 7 hour glass... when it runs out, you are at 9 minutes.

This, of course, assumes the sand falling out is linear with time... I'm not sure it is.

The "Democrat" answer is to say it's not fair that the 7 minute glass has more sand.... So you break the hour glasses and divide the sand equally... and you have more than 9 minutes and everyone wins.

That works too.

Other answers??? I know there is at least one. MM

 

[MonacoMike]

This is the answer I knew: Start both together. Flip over the four-minute glass when it runs out (at 4:00); and for the seven-minute glass (at 7:00). When the four-minute glass runs out the second time (at 8:00), the seven-minute glass will have one minute of sand in its lower bulb. Flip the seven-minute glass over again and let the minute of sand run back. When all the sand falls, that will be nine minutes. MM