Time Again

Est. Class Sessions: 1

Developing the Lesson

Part 2. Elapsed Time

Ask students to think again about the number of minutes in each hour. Ask them to look at their individual clock and count the minutes by 5s from 5 to 60.

Ask:

How many minutes are there in one hour? (60 minutes)
If there are 60 minutes in one hour, how many are there in 11/2 hours? (90 minutes)
How can you show this on your clock? (Possible response: If I start with the minute hand on the 60 and go all the way around once that is 60 minutes. Then I need to go halfway around again, or another 30 minutes. 60 + 30 = 90 minutes.)
How many minutes are there in 2 hours? (120 minutes) Explain how you know? (One hour is 60 minutes so two hours is 60 + 60 or 120 minutes.)
How many minutes are in 2 hours and 15 minutes? (135 minutes) How do you know? (If 2 hours is 120 minutes, you just add 15 minutes more to get 135.)

After students are comfortable finding the number of minutes in a given time interval ask them to find the number of hours and minutes represented when the time is given using only minutes.

For example, ask:

How many hours and minutes have passed in 150 minutes? (2 hours and 30 minutes)
How can you use your individual clock to show this? (If I move the minute hand around the clock once, that is 60 minutes. If I go around again, that is 120 minutes. I would have to go 30 more minutes to equal 150 minutes.)

Direct students to the Passing Time section in the Student Guide. These problems provide practice finding elapsed time using three different contexts. In Questions 3–6 and Questions 11–12, students are given the start and end time for an event and are asked to find the elapsed time. In Questions 7–8, the start time and duration of the event are given and students are asked to find the end time. In Questions 9–10, the end time and the duration of the event is given and students find the start time.

Before students begin to work on these problems, read the sample problem and discuss the strategies Luis and Carla used to solve the problem. Ask students to think about other strategies they could use to solve the problem.

Assign Questions 3–12. Students can work on these problems with a partner or they can be completed as a class. Encourage students to share the strategies they use to find each solution.

Student Guide: 152 153 154

Answers