Lesson plan

# 4. Solve time interval problems (A)

teaches Common Core State Standards CCSS.Math.Content.3.MD.A.1 http://corestandards.org/Math/Content/3/MD/A/1
teaches Common Core State Standards CCSS.Math.Practice.MP1 http://corestandards.org/Math/Practice/MP1
teaches Common Core State Standards CCSS.Math.Practice.MP4 http://corestandards.org/Math/Practice/MP4

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Lesson objective: Solve elapsed time problems where the starting time is unknown by using a number line to represent subtraction.

This lesson provides an opportunity for students to apply their knowledge and understanding of telling time and number operations to solve a real-life situation. Students are asked to determine the range of starting times for making brownies given the elapsed times and the ending time. Students use a number line to understand the problem, the meaning of the question asked, and show their methods for solving the problem.

Key Concept students will use:

• We can use representations such as a number line to solve situational problems involving addition and subtraction of time in minutes.

Skills students will use:

• a number line to show the time to the nearest minute and
• a number line to show how to subtract elapsed time.

Students engage in Mathematical Practice 1 (make sense of problems and persevere in solving them) as they use the number lines to show their methods for solving elapsed time problems.

Key vocabulary:

• elapsed time
• number line
• range of times

Special materials needed:

• Judy clock for demonstration
• Number line for demonstration
• Student clocks