Puzzle : Set Timer without Clock?

You are a cook in a remote area with no clocks or other way of keeping time other than a four-minute and a seven-minute hourglass. On the stove is a pot of boiling water. Jill asks you to cook a nine-minute egg in exactly 9 minutes, and you know she is a perfectionist and can tell if you undercook or overcook the egg by even a few seconds. 

How can you cook the egg for exactly 9 minutes?

You should follow THIS process! 

Solution : Setting up Timer without Clock!

What was the challenge?

We can set up a timer of 9 minutes using 4 and 7 minutes hourglass. Below is the process-

1. Flip both the hourglasses and drop egg into the water. 

2. After 4 minutes, 4-minutes hourglass will run out. Flip and reset it. ( 4 minutes counted and 3 minutes countdown left in 7-minute hourglass).

3. After 3 minutes, the 7-minutes hourglass will run out while 1 minute countdown will be left in 4-minutes hourglass. ( So far 4 + 3 = 7 minutes counted ). 

Flip the 7-minutes hourglass thereby resetting it's timer.

4. After 1 minute, the 4-minutes hourglass will run out. ( 4 + 3 + 1 = 8 minutes counted). 

5. At this point of time there will be sand for 6 minutes countdown left in 7-minutes hourglass. Just flip it so that it count exactly 1 more minute.
   

Now, that's how 4 + 3 + 1 + 1 = 9 minutes are counted.

 

An Experimental Professor

An eccentric professor used a unique way to measure time for a test lasting 15 minutes.
He used just two hourglasses. One measured 7 minutes and the other 11 minutes.
During the whole time he turned the hourglasses only few times. 

How did he measure the 15 minutes?

Couple of methods to count 15 minutes. 

Source 

15 Minutes Countdown

What was the challenge?

There were 2 ways for professor to count 15 minutes using 11 & 7 minutes hourglasses.

Method 1 :

1. He started both 7 & 11 minutes hourglasses but didn't begin test.

2. After 7 minutes hourglass ran out, he started the test. Still 11 one yet to count 4 minutes.

3. After conducting test for 4 minutes, 11 hourglass ran out.

4. Now he turns around 11 hourglass & continues. So 11 + 4 = 15 minutes counted.

Method 2 :

1. He started both the hourglasses & started to conduct the test as well.

2. When 7 minutes ran out he turned around it & kept 11 minutes counting.

3. After 4 minutes, 11 minutes hourglass ran out. Meanwhile 7 minutes hourglass also counted 4 minutes. So far 11 minutes counted.

4. Then he again turned around 7 minutes hourglass which had counted 4 minutes. That's how 7 minutes counted 4 minutes again.

5. In this way, 11 + 4 = 15 minutes counted.