perplexus.info :: Just Math : The hour-glass

The hour-glass (Posted on 2009-01-20)

An hour-glass is formed by two identical cones.

Initially, the top cone is full of sand, and the bottom cone is empty.

The sand starts flowing down at a constant rate and the top cone is emptied in exactly 1:30 hours.

How long does it take for the height of the sand in the bottom cone be half of the height in the top cone?

Submitted by pcbouhid

Rating: 2.5000 (2 votes)

Solution: (Hide)

1h 03min 20seg.

See Charlie´s solution here and the pertinent comment of rod hines here.

I agree with rod, the problem should state "water" or some other appropriate liquid, not "sand".

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
No Subject	Glenn Howard	2023-10-05 07:14:01
Puzzle Answer	K Sengupta	2023-10-05 00:34:33
re: Sand vs. Water?	Charlie	2009-01-21 11:24:18
Sand vs. Water?	rod hines	2009-01-20 17:21:29
solution	Charlie	2009-01-20 12:43:59

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