25 replies to this topic

[Lyzard]

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

2+7=9

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.

[samiam81]

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

T = 0min ---- Turn over the 4 and 7 minutes glasses.
T = 4min ---- The 4 runs out, Flip it. (3 minutes in 7 glass)
T = 7min ---- The 7 runs out, Flip it. (1 minute in the 4 glass)
T = 8min ---- The 4 runs out. 1 minute in bottom of 7 glass, Flip 7 glass.
T = 9min ---- The 7 runs out, 9 minutes reached +/- about 5 seconds to allow for flipping time.

[TiHokie]

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.

[Loaner]

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

Cpotting,

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.

[Trogdor]

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.

[kat800]

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