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?

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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.