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# 3-GM-3-2

last edited by 3 years, 8 months ago

3.GM.3.2 Determine the solutions to problems involving addition and subtraction of time in intervals of 5 minutes, up to one hour, using pictorial models, number line diagrams, or other tools.

In a Nutshell

In third grade, students are getting their introduction to elapsed time. It is vital that they understand that you can add or subtract time to help solve problems in real world contexts. Students need plenty of experiences with tools and strategies that will help them make the connections necessary for determining elapsed time.

## Teacher Actions

• Model time addition or subtraction using various tools such as a number line, pictures, and clocks.

• Develop strategies for problem solving, such as reading the context, drawing a picture, or acting out the problem, to accurately find the solution.

• Communicate solutions mathematically to peers and justify the answer using a variety of tools and strategies, such as skip counting or drawing a clock.

• Pose purposeful questions to help students recall prior knowledge and justify their thinking. Questions may include: What are some different ways to find the solution? How does this skill help us in our everyday life? How can we prove our answer? What clues helped you solve this problem?

• Implement real-life tasks where you would need to be able to add or subtract time. For example: Ricky leaves school at 3:25. It takes him 15 minutes to get home. What time is it now?

• Support productive struggle as students explore a variety of methods to solve the problems, such as number line instead of a clock.

## Misconceptions

• Time is considered a measurement. Because of that, time can be added or subtracted.

• When the hour or minute hand is moving “clockwise”, time is being added. When the hour or minute hand is moving “counterclockwise”, time is being subtracted.

• When the minute hand passes the 12 on the clock, they have moved to the next hour.

• When the hour hand moves from 12 to 1 o’clock, a.m. turns to p.m. or vice versa.

• They can just add time like regular numbers. For example: If you start at 11:50 and you add 20 minutes, the time would be 11:70.

• Only the minutes change when adding or subtracting time. For example: If you start at 4:40 and you add 30 minutes, the time would be 4:10.

OKMath Framework Introduction