standard_description: Use addition and subtraction within 20 to solve word problems involving situations of adding to, taking from, putting together, taking apart, and comparing, with unknowns in all positions, e.g., by using objects, drawings, and equations with a symbol for the unknown number to represent the problem.
problem_activity: Narrative
In this activity, students encounter another type of elapsed-time problem in which the start and end times are given but the elapsed time is not. Students consider possible strategies they saw earlier that could be used to find elapsed time. Although they are not required to solve the problem, students may choose to do so as they think about ways to reason abstractly and quantitatively about the solution (MP2).
Launch
Groups of 2
Read the problem as a class.
“How is this problem like the ones we saw earlier?” (They are all about the passing of time and are related to riding the bus. The start time is given in all of them.) “How is this one different?” (The arrival time is given here, and the amount of time that has passed is missing.)
1 minute: quiet think time
Share responses.
Activity
“How would you solve this problem? Explain which strategies or representations you saw earlier that would be useful for solving a problem like this.”
5–7 minutes: independent work time
Student Facing
Here’s another problem about time:
At 6:32 p.m., Elena got on a bus to go home. She got off the bus at 7:10 p.m. How long was her bus ride?
Which strategy or representation would you use when solving a problem like this? Explain your reasoning.
Student Response
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Activity Synthesis
Invite students to share their reasoning and strategies. Display or record different representations for all to see.


aligns: no