Personal Comment: Not hard since you are allowed to flip them over whenever you want.

Hourglasses Enigma

What we know: You have two hourglasses--a 4-minute glass and a 7-minute glass.

Enigma: How do you measure 9 minutes?

Solution: Start both hourglasses. When the 4-minute glass runs out, turn it over (4 minutes elapsed). When the 7-minute glass runs out, turn it over (7 minutes elapsed). When the 4-minute glass runs out this time (8 minuts elapsed), the 7-minute glass has been running for 1 minute. Turn it over once again. When it stops, 9 minutes have elapsed.

See who got this right

Previous Enigma | Enigma Index | Next Enigma

This window to the Fourth Dimension is hosted by Geocities