Problem Pictures
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PP2 CD-ROM cover

This picture is taken from Problem Pictures Themes, a CD-ROM of photographs with activities for mathematics teaching.

Egg timer

When you turn over this egg timer, three sand timers measure 3 minutes, 4 minutes and 5 minutes. They cannot be turned over individually.

How could you use the timer to measure 6 minutes?

You could measure 7 minutes by adding together 3 and 4 minutes - but does it matter which you do first?

Is it possible to measure 2 minutes? Is it possible to measure half a minute?

What other times could you measure? What if you had three separate sand timers?


The photographs and screen images on this website are copyright and may not be reproduced without permission. Copyright Richard Phillips 2001/2007. Page updated 13 July 2005.