standard_description: Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.
problem_activity: Narrative
The purpose of this activity is for students to learn stage 2 of the Estimate and Measure center. Students estimate and measure the length of objects. This stage includes centimeters, inches, and feet. Students should only measure in centimeters at this point in the unit. In this activity, students also find the difference between their estimate and their measurement for extra practice.
Required Materials
Materials to Gather
Metersticks
Objects of various lengths
Rulers (centimeters)
Materials to Copy
Estimate and Measure Stage 2 Recording Sheet
Required Preparation
Gather or identify objects of various lengths (pencils, markers, books, glue, scissors, shoe, tape dispenser, side of desk, length of bulletin board).
Launch
Groups of 2
Give students access to centimeter rulers and meter sticks.
Give each student a recording sheet.
“We are going to learn a new center called Estimate and Measure. Today we are going to estimate and measure the length of different objects.”
“First you and your partner will decide on an object in the room to measure. Then you will decide what tool you will use to measure the object.”
Choose an object to measure and hold it up for students to see.
“What tool would you use to measure this object?”
“Before measuring the object, you and your partner will both estimate the length of the object using the unit you chose. Your estimates do not have to be the same. Record your estimate.”
Demonstrate estimating the length of your object and recording it on the recording sheet.
“Now work with your partner to measure the object and record the actual measurement.”
Demonstrate measuring the object, thinking aloud as you line up the endpoints and use the number on the tool to determine the length.
Record the actual measurement on the recording sheet.
“If you have time: Once you have estimated and measured the object, find the difference between your estimate and the actual length.”
Demonstrate finding the difference.
“Put your object back and choose another object to measure.”
Activity
10 minutes: partner work time
Activity Synthesis
Display a row of the recording sheet with this information:
Object: notebook
Estimate: 20 cm
Actual Measurement: 31 cm
“How can we find the difference?” (We can add on to 20 until we get to 31. We can subtract 20 from 31.)


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