self Maths Puzzle

You need to boil eggs for exactly 9 minutes, or else the visiting Duchess will complain, and you will lose your job as head chef.

But you have only 2 Hourglasses, one measures 7-minutes, and the other measures 4-minutes. How can you correctly measure 9 minutes?

Read Solution (Total 1)

Put the eggs on to boil and start both hourglasses running.

When the 4-minute one runs out, turn it over immediately so it starts counting 4 minutes again

When the 7-minute one runs out, turn it over so it starts counting 7 minutes again

The moment the 4-minute one runs out for the second time, turn the 7 minute hourglass over - it will have only been running exactly one minute.

Let the sand run back again (1 minute more) and then take the eggs off straight away, because they will have boiled for 9 minutes.

(4 minutes twice, plus one more minute = 9 minutes!)
4 years agoHelpfull: Yes(0) No(0)

self Other Question

The founders of Hairytown decreed years ago that:

1. No two people can have the same number of hairs
2. No one can have 999 hairs.
3. No one can have more than, or the same number of hairs as, the population of the town

The town has now reached its maximum population - what is it?
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 3 times.

How did he measure the 15 minutes?