The purpose of this activity is for students to solve problems involving addition and subtraction of time intervals when given times on a clock. Students may choose to show or explain their reasoning in any way, but the clocks are given to encourage use of that representation. Monitor for different ways that students represent their thinking, particularly differences in strategies when the problem involves time crossing the hour mark versus when it doesn’t.

• Select previously identified students to share their responses and reasoning.
• “We noticed that when the time does not cross the hour, we can just add or subtract the number of minutes, such as here. When the time does cross the hour in a problem, we need to make sure to keep track of what hour we are in.”

The purpose of this activity is for students to solve problems involving addition and subtraction of time intervals in minutes. Students fill a name and an activity into each problem before they solve it using any representation that makes sense to them. The Activity Synthesis draws attention to the different types of problems that have been solved. Students need to read and think carefully about the given information and the unknown, which differ in most of the situations, in order to decide which calculations to perform (MP2).

• For each problem, invite groups to share what they filled in and how they solved the problem.
• Keep the problems displayed.
• “How are these problems alike?” (They are all about doing an activity for a certain amount of time.)
• “How are they different?” (They are about different activities and give different kinds of information. Sometimes we know the start time and end time. Other times we know either the start time or end time, and how much time passed. We are solving for different things.)
• Highlight ideas about how the problems had different unknowns (start, end, and time that passed).