Jump to content

Welcome to BrainDen.com - Brain Teasers Forum

Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.

Of course, you can also enjoy our collection of amazing optical illusions and cool math games.

If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.

Thanks and enjoy the Den :-)
Guest Message by DevFuse

- - - - -

Sand-glass I.

  • This topic is locked This topic is locked
25 replies to this topic

#21 Lyzard



  • Members
  • Pip
  • 1 posts

Posted 02 May 2008 - 04:06 PM

there is a much simpler meathod.

it says corectly time 9 mins with the two glasses, it never says you have to use them at the same time.

so start the 4 min glass, when that is half gone, start the 7 min glass


much faster and much less hassle then to stand there and flip the glasses several times.

Aseatha85 is correct. Never did it mention that you were to time 9 minutes on EACH glass.
  • 0

#22 samiam81



  • Members
  • Pip
  • 9 posts

Posted 28 May 2008 - 09:50 PM

For those who claim to turn over the hour glass half way through, have you ever tried to guess the halfway point an hourglass? I find it extremely hard to compare the estimated the volume of sand in the top and the bottom. If you are not skilled at "guessing" the halfway point of the 4 minute hourglass than you could be as much as a minute off.

Spoiler for Hourglass

  • 0

#23 TiHokie



  • Members
  • Pip
  • 2 posts

Posted 05 June 2008 - 05:49 PM

How about this...

T-0 = Start both hourglasses
T-4 = 4 runs out, restart it (3 minutes left in the 7m HG)
T-7 = 7 runs out, restart it (1 minute left in the 4m HG)
T-8 = 4 runs out, restart it (6 minutes left in the 7m HG)
T-12 = 4 runs out, restart it (2 minutes left in the 7m HG)
T-14 = 7 runs out, restart it

Steps T-12 and T-14 give you the nine minutes - and yes, you have to wait 12 minutes to start timing for the 9. It beats playing with the idea the you can accurately measure when half of the time is measured. If your solution is to say flip it at the half way mark, then you might as well say flip the 4m HG three times and then stop when 1/4 of the sand is in the bottom after the third flip.
  • 0

#24 Loaner



  • Members
  • Pip
  • 3 posts

Posted 18 August 2008 - 09:55 PM

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


I read your post and had to explain why I was laughing hysterically at my desk. My reply of "9 minutes takes 9 minutes" didn't seem to quell the worrying looks I was getting. But I don't care, that was funny.
  • 0

#25 Trogdor


    Junior Member

  • Members
  • PipPip
  • 36 posts

Posted 22 August 2008 - 06:52 PM

I think there is a faster way to do this..

Start with both the hr glsses. At the end of 4 minutes keep the 4min glass inverted and wait for the 7min hr glass to get empty. When the 7min glass is empty keep it in inverted position. After 1 minute, totally 8 minutes have passed. Now invert the 7min hr glass. And u have 4 + 4 + 1 =9.

Tell me if its not right.

I'm pretty sure that there is no faster way of measuring time...

Edit: Just read the comment above...

Edited by Trogdor, 22 August 2008 - 06:54 PM.

  • 0

#26 kat800



  • Members
  • Pip
  • 3 posts

Posted 18 October 2008 - 02:09 AM

If you were to take the four min glass and turn it over on it's side you could tell with much more accuracy when it is half way done, then stop it at two minutes. Next turn over the seven minute glass. It seems to me that this is much simpler. 2+7=9
  • 0

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users