DS, who is 7, has just done 25 or so sums along the lines of
149+376+458
I'm not sure if he was supposed to do them in his head or with working out, as there is no space on the worksheet for any working, but as I think faculty with mental arithmetic is useful, I've not told him to do them outright.
He got about 20/25, but had made some obvious mistakes such as '1007' as the answer to the above - to which I asked him what 9+6+8 is, to show that the answer could not end in 7.
I'm wondering what the best way to advise him to do such sums mentally is - either 100+300+400= 800, then add 40+70+50 - 160, then 9+6+8 = 23. Or just 149+376 = 525, then 525+458 = 983
He's obviously quite good at it, but I think the 20% error rate is too high to be justifiable. Just practice and let him work it out by himself? Do it twice?
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Primary education
Mental arithmetic techniques
5 replies
SomeGuy · 09/10/2009 17:09
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