Stage: 2 Challenge Level: 
You have two egg timers.
One takes 4 minutes exactly to empty and the other takes 7 minutes.
What times in whole minutes can you measure and how? (You can ignore the time it takes to reset the timers.)
Visualising. Trial and improvement. Factors and multiples. Addition & subtraction. Investigations. Multiplication & division. Working systematically. Interactivities. Practical Activity. Combinations.
Published March 1998.
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