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Q&A #4824

Teachers' Lounge Discussion: A different way to subtract than normally taught

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From: Ngaire <nhynd@hotmail.com>
To: Teacher2Teacher Public Discussion
Date: 2009082321:43:02
Subject: Re: Re: A different way to subtract than normally taught.


Thankyou Frances! You are the first person I have "met", other than my
brother and my Dad (who was our schoolteacher!) who uses the
Compensation Method! I am Australian and we were taught this method in
the 70s and 80s. EVERY maths curriculum I have looked at since (We
homeschool our children) uses borrowing and it is soooooo clumsy. I do
see that borrowing is an easier concept to grasp, but if the child can
only get what we are doing when compensating, the method is then
forever after soooo much speedier!
We were taught thus:

34-
18

Add ten to the 4 in the units column so that we can take away 8: 
14(units) - 8(units) = 6 (units).
Then compensate for that "extra" addition of ten by taking away an
extra ten in the tens column: 3 (tens) - 2 (tens) = 1 (ten). Answer:
16.

We wrote a tiny little "1" up in the air just to the left of the 4 so
that it looked like "14" (with the 1 tiny and up in the air) and a
tiny "1" under and just to the right of the "1" in the tens column to
remind us to take away an extra ten. So quick!!

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