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Which method for 2 digit subtraction sums?

(6 Posts)
tiredbutnotweary Thu 20-Feb-14 22:04:43

The question was how many more eggs did the hens lay on Saturday compared to Sunday (i.e. what's the difference). DD knew the sum to get the answer was 22 - 16, however DD can't do this in one step.

I am wondering which method is taught at school - or would either be acceptable? I think she'd find the second one easier because she's more confident with addition however would this go against how they're normally taught (not a natural mathematician here and it's not parent's evening for a while!!!)?

22 - 10 = 12 then 12 - 6 = 6

or

16 + 4 = 20 then 20 + 2 = 22 then 4 + 2 = 6

bsmirched Thu 20-Feb-14 22:09:39

I would think she'd be best counting on from the lower number ie 16. Definitely encourage her to first count on to the next ten, then to 22 as in your second method. She has more than likely been shown how to do this as 'jumps' on a number line.

VelmaD Thu 20-Feb-14 22:11:01

How old is she?

Ds2 has been doing these kind of sums and the school favours using a hundred number square. We've also done number line style. He's five and year one.

ReallyTired Thu 20-Feb-14 22:14:08

Most children learn the column method eventually however it is taught a lot later than when we were at school. (ie. year 2 year 3) In the mean time they are taught load of other methods which are more work, but easier to understand.

RafaIsTheKingOfClay Thu 20-Feb-14 22:21:48

Counting up will be fine for finding the difference between two numbers that are close together. it's probably what the school would teach but both methods will be taught at some point. It's really up to her which method she chooses.

tiredbutnotweary Fri 21-Feb-14 09:46:53

Thank you!

She'd have no problem using a number line or square.

Doing it mentally following method 1 & DD's working memory hit it's limit (I was cooking & she was wanting to help & do the sum too otherwise it might not have come up) so later I wondered if counting up would have been easier for her.

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