Nine to one

Here is a trick which would make a great start to a maths lesson. The mentaloral part of the lesson dictates the pace and bounce of the whole lesson so it is vital that we capture children's attention and excitement right from the start. It fits nicely into parts of the Numeracy Strategy or can be used as a stand alone.

This puzzle will enable children to become mind readers and is based on the nine times table.

Think of any number between 11 and 19. Add together the two digits in the number. Then take the second answer away from the first. The answer will always be nine.

So, if for example, you chose 11, you would add one and one to give two, then take it away from 11 to give nine. Here are all the numbers: 11 - 2 = 9; 12 - 3 = 9;

13 - 4 = 9; 14 - 5 = 9;

15 - 6 = 9; 16 - 7 = 9;

17 - 8 = 9; 18 - 9 = 9;

19 - 10 = 9

To extend the more able pose the following questions: what will the answer always be for numbers between 21 and 29, 31 and 39, 41 and 49, 51 and 59, 61 and 69, 71 and 79, 81 and 89, 91 and 99.

21-29 = 18; 31-39 = 27; 41-49 = 36; 51-59 = 45; 61-69 = 54; 71-79 = 63; 81-89 = 72; 91-99 = 81

* All the answers add up to 9. For instance, 1+8 = 9, 2+7 = 9.

* The units (or 1s) column descends in 1, for instance 8, 7, 6

* The tens column increases in 1s, 1, 2, 3, etc

* 18 is the reverse of 81, 27 is the reverse of 72, 36 is the reverse of 63: another pattern to identify. IA

Isaac Anoom is a consultant and teacher at Donnington primary, north-west London

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