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## 'What Was in the Box?' printed from http://nrich.maths.org/

A number in a little box is put into a wonderful big box that adds something to the number and then a new number comes out at the end:

The first time this happens, 10 is put into the little box, so what happened in the big box to get the answer in the picture above?

Now three more boxes with new numbers in, go into the wonderful box one at a time. It still does the same as before.

So, what were the three new numbers that went in? Remember that the wonderful big box did the same for all four numbers that went in.

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Imagine four new boxes now (with new numbers in) and the wonderful box does a new and different add or take away this time. For one of these boxes the number 10 was put in. The numbers that come out are these:

What could have happened? How did you work these out?

Discuss with others and see if there were different ways that you found the answers.