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# Sand-glass I.

25 replies to this topic

### #11 BoilingOil

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Posted 27 September 2007 - 03:56 PM

Although, peachykeen, yours is the only answer anyone can understand, nine min. could be timed a bit faster using a similar method.

-Start both timers

1. When the 4 min. glass is done, start it again. (The 7 min. glass now has 3 min. left to count)

2. When the 7 min. glass is done, start it again. (There will be one min. remaining on the 4 min. glass and the 7 min. glass will now be counting that one min.)

3. When the 4 min. glass is done, the 7 min. glass will now have just one min. worth of sand on the bottom, turn it over and that sand will count the remaining min.

1. 4min. (from the 4 min. glass)
2. 3min. (from the 7 min. glass)
3. 1min. + 1min. (the first from the 4 min. glass, the second from the 7 min. glass)

We're trying to time 9 minutes! How can that ever be done faster than in exactly 9 minutes, huh? None of the methods could ever claim to be faster than any of the others. They could at best be simpler to use, simpler to understand even.

In that respect, b.t.w., your method wins by all means. Very clear, and easy to understand. Even for me

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Posted 28 September 2007 - 01:44 PM

We're trying to time 9 minutes! How can that ever be done faster than in exactly 9 minutes, huh? None of the methods could ever claim to be faster than any of the others. They could at best be simpler to use, simpler to understand even.

In that respect, b.t.w., your method wins by all means. Very clear, and easy to understand. Even for me

BoilingOil

Several people, so far, have commented on having "faster" ways to solve this problem.

I'd just like to point out, that ALL these methods take 9 minutes. None of them are "faster".

pedantic, but true

There are faster ways of timing 9 minutes. The 9 minutes alone obviously take the same amount of time. But rookie's answer takes only 9 minutes. peachykeen's answer adds 7 minutes to the front of that for a total of 16 minutes.

Again, pedantic, but right <!-- s;) --><!-- s;) -->
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### #13 irokhardfm1

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Posted 27 November 2007 - 03:38 PM

First.... You get a stop watch, press start wait for 9 minutes then press stop...
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### #14 aishi_khurana

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Posted 10 December 2007 - 08:59 AM

I ve an easier answer to this...first you turn both the glasses upside down...wen 4 minutes r over then turn d glasses....we'll b left with 1 minute of sand in 4 minutes glass....now keep d 7 minutes glass aside and let d 1 minute of sand flow...wen the last grain is left turn the glass upside down nd repeat the same process ftr 4 min. of turning it again....we get 9 minutes...1+4+4...i hope it's right?
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### #15 Will

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Posted 29 December 2007 - 06:51 PM

Start both glasses at the same time.
turn 4 min glass over when it stops, giving you 8 mins.
When the 7 min glass stops, turn it over.
Then turn 7 min. glass over once again after 4 min. glass is finished with 8 mins., giving you 1 more minute.
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### #16 superbc

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Posted 22 February 2008 - 05:27 PM

Sand-glass I. - Back to the Water and Weighing Puzzles
Having 2 sand-glasses: one 7-minute and the second one 4-minute. How can you correctly time 9 minutes.

Spoiler for Solution

Start both the 7 and 4 minute at the same time.
Stop both when the 4 is complete. You will have 3 left in the 7 glass.
Start the now 3 and 4 at the same time.
Stop when the 3 is complete. You will have 1 left in the 4 glass.
Start the 7 and now 1 at the same time.
Stop whe the one is complete. You will have 6 in the 7 glass.
Start the now 6 and 4 at the same time.
Stop when 4 is complete. You will have 2 in the 7 glass.
Start the now 2 and 4 at the same time.
Stop when the 2 is complete.
You now have a full 7 and a half 4 equaling 9.
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### #17 desertdude

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Posted 04 March 2008 - 09:11 PM

[quote name='rookie1ja' date='Mar 30 2007, 06:43 PM' post='83']
Sand-glass I. - Back to the Water and Weighing Puzzles
Having 2 sand-glasses: one 7-minute and the second one 4-minute. How can you correctly time 9 minutes.

you let the 7 min go past all the way and let the 4 min go half way
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### #18 needve

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Posted 28 March 2008 - 02:05 AM

So will all these solutions work if the sand is nonlinear? They have been timed to complete the whole time, but not when they are flipped over mid way. For example if you start the 4 and 7 at the same time and at the end of the 4 min, you turn the 7 over it may not take 4 min for the 7 to run back out. If so what type of relationship might hold? I have no idea.
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### #19 sunshipballoons

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Posted 02 April 2008 - 12:25 AM

Several people, so far, have commented on having "faster" ways to solve this problem.

I'd just like to point out, that ALL these methods take 9 minutes. None of them are "faster".

pedantic, but true

Well, since we're going to be pedantic, I will point out that none of them IS faster.
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### #20 brainwwings

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Posted 04 April 2008 - 12:55 PM

Turn the 7 min glass over, let sand run to bottom.

Turn the 4 min glass over, when there's an equal amount of sand on top or bottom, 9 minutes have passed.
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