Q&A #522

Teachers' Lounge Discussion: Teaching subtraction

T2T || FAQ || Ask T2T || Teachers' Lounge || Browse || Search || Thanks || About T2T

View entire discussion
[<< prev]

From: Diane <diane.canavan@ozemail.com.au>
To: Teacher2Teacher Public Discussion
Date: 2006080410:27:37
Subject: Re: teaching subtraction

How to teach a year 2 child to do borrowing rather begs the question,
why?  At this age children are far better occupied developing
intuitive strategies based on a full understanding of subtraction.  It
is not just take-away, but also "difference".  This understanding
allows children to use the relationship between addition and
subtraction to solve problems.  The easiest way to solve subtractions
involving zeros is to "build-up" to the tens or hundreds.
For example 300 - 189.
 From 189 you need to add 1 to go to 190.
 From 190 you need to add 10 to go to 200.
 From 200 you need to add 100 to go to 300.
The difference between 300 and 189 is therefore 1 + 10 + 100 = 111

That said, if you have to do borrowing I have a way, if the children
understand place value.  Consider again 300 - 189.
Subtracting the units first we see 0 - 9, which can't be done.  When
you go to the next digit it is also 0...no help.  
The three hundreds can be thought of as 30 tens.  You can take one of
these tens leaving 29 tens.  
Cross out the 30 and replace it with 29. Give the ten to the units.

Then 10 - 9 = 1,  9 - 8 = 1, 2 - 1 = 1.   Again 211.

Post a reply to this message
Post a related public discussion message
Ask Teacher2Teacher a new question

[Privacy Policy] [Terms of Use]

Math Forum Home || The Math Library || Quick Reference || Math Forum Search

Teacher2Teacher - T2T ®
© 1994- Drexel University. All rights reserved.
The Math Forum is a research and educational enterprise of the Drexel School of Education.The Math Forum is a research and educational enterprise of the Drexel University School of Education.