Reflection: Complex Tasks Let's Compare - Section 3: Independent Practice


Comparison problems are more complex than simple subtraction problems.

First, all word problems are really two-part problems - the first problem is determining which operation to use and the second problem is actually performing the operation.  Students are expected to recognize the problem and solve it by putting together or taking apart (2.OA.A1) The difficulty with comparison word problems in particular is that no “action” is being performed - no putting together or taking apart. Students do need to find the difference and conceptually, that is a difficult concept.

Students understand how to carry out a subtraction problem, but when asked to compare 2 objects they have trouble deciding whether to add or subtract. Visually I can show the students that if they add they will have an answer bigger than they started with, and that would not be a comparison. I often do this with snap blocks. I show a tall tower and a smaller tower. I ask how much taller the first is than the second? I put one tower on top of the other and say would the small one be THAT much taller? (NO - they all see that). So then how can I find the difference? (count up from the small to the tall, or subtract the small from the tall). 

The comparison is something that must be shown visually before students can understand what the idea of bigger than or smaller than is really asking them to do.

  Complex Tasks: Comparisons
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Let's Compare

Unit 12: More Complex Numbers and Operations
Lesson 8 of 10

Objective: SWBAT take two objects and compare them using mathematical equations.

Big Idea: A comparison is not the addition of two numbers, but a difference. Seeing the visual difference is the focus of this lesson.

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