Math: Subtraction

12 04 2010

We’ve been hard at work doing subtraction. Difficult problems up to four places, and even-more-difficult word problems. Floppy is getting pretty good at carrying, and is — to me at least — impressively good at using his fingers to subtract numbers.

Some pictures:

Hard at work

on these head-scratching problems

Getting ready for the grand finale word problem….

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One response

10 12 2010
ZeroSum Ruler

This might not be too useful for multi-digit problems, but I learned an awesome model for subtraction today at an interview, of all places. The “as compared to” model. Take “7 – 2”. This can be read as “7 as compared to 2”, which leads to an answer of “they are comparably 5 apart”.

It also works for subtracting negatives! “7 – -2” can be read as “7 as compared to -2”, which leads to an answer of 9 since 7 and -2 are comparably 9 spaces apart!

So awesome!
http://zerosumruler.wordpress.com/

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