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Step 2Match pairs
What is special about the pairs (1 and 9), (3 and 7), (4 and 6)?
They sum to 10. There are only five of these pairs so anyone who has spent a while doing maths should instantly recognise them, and they can make your life a whole lot easier when doing additions.
Take 13+27. Recognising the matched pair 3 and 7 in the ones place tells you the answer will be a multiple of ten, so you have to add 10, 20 and the 10 resulting from (3+7) to get 40- you have effectively simplified the addition from 13+27 to (1+2+1) * 10. Good for you.
If you become proficient at this technique, you may be able to combine it with the previous technique- if you saw 14+25 you might recognise that you can borrow a one to turn it into 14+26 then use this technique.
Pros: very quick, conceptually simple, quite general
Cons: requires practise for recognition, slightly limited application.
They sum to 10. There are only five of these pairs so anyone who has spent a while doing maths should instantly recognise them, and they can make your life a whole lot easier when doing additions.
Take 13+27. Recognising the matched pair 3 and 7 in the ones place tells you the answer will be a multiple of ten, so you have to add 10, 20 and the 10 resulting from (3+7) to get 40- you have effectively simplified the addition from 13+27 to (1+2+1) * 10. Good for you.
If you become proficient at this technique, you may be able to combine it with the previous technique- if you saw 14+25 you might recognise that you can borrow a one to turn it into 14+26 then use this technique.
Pros: very quick, conceptually simple, quite general
Cons: requires practise for recognition, slightly limited application.
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