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Adding up – Quickly!


Do you ever find yourself adding up a long list of numbers – checking a receipt maybe – and when you get to the end, you are not sure you included that 42 near the top? Or maybe you are halfway through and your dog jumps up at you, or you get a text you need to check?

Were you adding on each number at a time?
23 plus 145 , Hmm  168..  now add on 283..  that makes… Lets look at a quicker way.

 

 

We would normally add up one column at a time. But we can go further than that….

Look for sets of numbers that add up to 10. I’ve made a start here with the 7 and the 3.

 

 

Then I have collected together the two 5’s and the 8 and the 2

Sometimes its not two numbers that add up to 10. Sometimes it can be 3 numbers, like the 1, 4 and 5

Of course not all numbers can be grouped in 10s. The last three numbers here are the 3, 3 and 1 and we can add them together to make 7 with a low risk of being interrupted.

We do need to count up how many sets of 10 we had. I counted 4. That is what that small 4 is doing at the foot of the second column…. and to be included in the ‘groupings’ of course .

The second column can be added up in the same way

And here we have more left over numbers, but still easier than adding them all up!

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