Q&A #16511

Modeling Subtraction of Integers using Red and Yellow Counters

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

View entire discussion

From: Mimi <mimisolis@comcast.net>
To: Teacher2Teacher Service
Date: Jan 14, 2006 at 03:19:12
Subject: Modeling Subtraction of Integers using Red and Yellow Counters

Modeling -7 - 5 using red(-) and yellow(+) counters is a difficult concept
to instruct.  How can this best be described so that students can fully
understand, therefore, accept the answer as -12 and not -2, -7 or some other
integer?  Students understand that they are subtracting 5 positive counters
from 7 negative counters, but they don't want to accept -- for they don't
understand -- that they have to add both red and yellow counters to the
model so that it doesn't change the value of the number they are
subtracting (in this case -7).

My model would show 7 red counters and then 5 red and 5 yellow counters to
illustrate that the value of -7 remains the same.  When I explain this, I get
perplexing facial expressions. They simply want to show 7 negative counters
and 5 positive counters. They understand the concept of additive inverse, but
they don't know that they need to apply it when subtracting a positive
integer from a negative one. They really don't understand the idea of why the
value of -7 in this problem must remain the same.  They just don't understand
what I am talking about here. How can I better describe this when modeling
subtraction of integers using red and positive counters so that they
understand that they are subtracting a positive number from a negative

Thank you for helping!

Post a 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- The Math Forum at NCTM. All rights reserved.