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# How good is your calculator?

David_Morgan 23 March 2007 10:15 - Last edited by David_Morgan on 23 March 2007 10:18
Posts115
Joined22/01/07

Children not only enjoy discovering that teachers are fallible but that their treasured calculator can do silly things.

If you have a super-duper calculator, this won't work! But many of the calulators we have in schools do not remember beyond six decimal places. So try this:

1 / 7 x 7 = some calculators give the expected answer of '1', but others will return '0.9999997' or something similar.

This simple exercise can lead naturally on to the discovery of recurring numbers and the particularly interesting recurring decimal approximation of 1/ 7.

This 6 figure number (.142857) has 'magical' properties as most year 4+ pupils will discover. Try multiplying it by 2 or 3 or 4 or 5 etc and look at the result. They will be intrigued!

David Morgan

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Mathemagician 02 June 2007 05:58
Posts152
Joined06/05/07

Good point David. Whenever my pupils bring a calculator to school I ask them to work out

1 + 2 x 3 =

If their calculator returns a value of 9 I ask them to get rid of it!

As you say, it can lead to some interesting discussions, in this case about BIDMAS (horrible word, that) and brackets.

Andrew

andrewjeffrey.co.uk

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HeatherNorth 31 July 2007 11:30
Posts244
Joined07/09/06
I think it is useful to remember how to use the calculator to highlight different aspects of number in these interesting ways ...I liked doing 1 / 9 = 0.1111111 then 2 / 9 = 0.22222222 and so on ..... guess what all the pupils said when we got to 9 / 9?  Maybe others can join this conversation to include some more examples we could use.  Thanks for starting this thread.  Heather
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