Friday puzzle -- nine-minute egg

Re: Friday puzzle -- nine-minute egg

Bill Earl

I can see a way to do it in 21. Is there a shorter way?

Re: Friday puzzle -- nine-minute egg

Bill Earl

Make that 16.

Re: Friday puzzle -- nine-minute egg

John Veerkamp

Start the 4 min timer. When it is 1/2 done start the 7 min timer.

Keep going

Alex Y

21 is the best I could do, but it's possible to beat your 16-minute method.

  no

Alex Y

No way to tell when the four-minute one is half done.

16 is easy

steven antonucci

start the 4 and the 7 together. when the 4 is empty, flip the 4. There was 3 in the 7, so when that is empty, there will be 1 left in the 4.

(ET of

when the one is empty, just use the 4 2 more times to get 1+4+4=9

ET of 16, wasting 7m to get to the 1 you need in the 1+4+4 eq...

Can't see a way to do it faster though. Please post if you have one...

S

Would you believe 13?

Bill Earl

Start the 4 and the 7.

put the egg in and flip the 4 when the 4 is empty.

In 3 minutes when the 7 is empty, flip that.

In one minute, when the 4 is empty, flip the 7 back.

In one minute when the 7 is empty again, start the 4.

That's 3+1+1+4 = 9

Hint

Alex Y

When you have the answer, you will be able to demonstrate not only that it works, but that it is the best possible solution.

Re: Friday puzzle -- nine-minute egg

Harvey Meyer in Atlanta

put egg in water and start both timers. After 4 minutes, the 4 min timer is empty and the 7 min timer has 3 minutes left. Flip over both timers. The 7 minute timer will be dumping 3 minutes of sand onto the 4 in the bottom. When the 3 minutes of sand are done, flip that timer again. When the 4 minute timer has finished, the 7 minute timer will have dumped 1 minute of sand. Flip the 7 minute timer once more and there will be one minute of sand to be dumped. When it's done you have a 9 minute egg in 9 minutes. That's my story and I'm sticking to it.

VERY close

Alex Y

You have the right idea, but made one error in your method.

Re: VERY close

Harvey Meyer in Atlanta

Hate to disagree, but I think it's right. However, since you're the judge, here's another method:

First, flip both hourglasses over and drop the egg into the water. When the four minute timer runs out, flip it over again. When the seven minute timer runs out, flip it over. The egg has been cooking seven minutes.

Now when the four minute timer runs out again (after eight minutes) flip the seven minute timer over again. Since the seven minute timer has been running only a minute between flips, there's a minute worth of sand left. And when that minute runs out, the egg will have been cooking for nine minutes. A 9 minute egg in 9 minutes. This is the same result in my first answer.

oops - you're right

Harvey Meyer in Atlanta

I see the error. My 2nd solution should be correct. Mea culpa.