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Money Measure

Stage: 2 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

Money Measure

You have ten identical open-topped boxes with 10 visually identical coins in each.

In nine of the boxes each of the 10 coins has a mass of 10g.
In one box the 10 coins have masses of only 9g each.

How can you find which box is the odd one out?

You have a normal mass measurer with a single pan and a scale. With just one weighing you can identify the box with the lighter coins.


boxes and scales

What will you weigh?


Why do this problem?

This problem involves thinking 'out of the box'. The pupils need to work out a way of making one weighing of all the boxes that will give them information about all the different boxes at once.

Possible approach

Key questions

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Possible support