[andrewas]

I dunno if that would work. Hourglasses are shaped so most of the sand would fall trough at 45 degree.

Anyway, my solution.

Turn over the seven and the four. When the four runs out, flip it. When the seven runs out, stop the four. You now have one minute in the four. Run the seven for one minute. You now have six minutes left on the seven.

Run the four and the seven to get two minutes remaining in the seven. Run the four and the seven again to get two minutes remaining in the four. You now have a four minute hourglass with two minutes in it, and a seven minute hourglass with seven minutes in it. Run those one after the other, and you have nine minutes.

EDIT] My previous solution was more elegant, because I was using the wrong numbers.

[ 02-21-2003, 03:30 PM: Message edited by: andrewas ]