Lesson 12
Hours, Minutes, and Seconds
Warmup: What Do You Know about 1 Hour? (10 minutes)
Narrative
The purpose of this warmup is to invite students to share what they know about 1 hour and its relationship with other units of time. The work here prepares students to convert units of time and solve problems later in the lesson.
Launch
 Display “1 hour”.
 “What do you know about 1 hour?”
 1 minute: quiet think time
Activity
 Record responses.
Student Facing
What do you know about 1 hour?
Student Response
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Activity Synthesis
 “Other than using hours, in what other ways can we measure time?” (minutes, seconds, days, months, years, decades)
 “When might it be more helpful to use hours than to use other units? When might it be more helpful to use minutes or seconds?”
Activity 1: Mai’s School Day (20 minutes)
Narrative
This activity develops students’ understanding of hours and minutes as units of time and helps them to see 1 hour as 60 times as long as 1 minute.
In converting hours into minutes, students may reason additively when the time in hours is a low singledigit number, but are likely to reason multiplicatively when converting, say, 8 or 10 hours into minutes. When they relate the operation of multiplication by 60 to converting hours to minutes, students make use of structure (MP7). To convert fractional numbers of hours (\(\frac{1}{2}, \frac{1}{4}\), and \(\frac{3}{4}\) hour), students might choose to think in multiplicative terms (for instance, \(\frac{1}{2} \times 60\)) but are not expected to do so. Instead they can rely on their prior knowledge about a quarter of an hour and a half of an hour to reason about the number of minutes.
Advances: Speaking
Launch
 Groups of 2
 “On a weekday, how do you spend the hours between the time you wake up and the time you go to bed? How much time do you spend getting ready for school, going to school, and at school? How do you spend your time after school?”
 “Take a quick minute to list your usual weekday routine, knowing that it may vary from day to day. You may choose to focus only on one day—say, Monday.”
 1–2 minutes: quiet think time
 1–2 minutes: partner discussion
 “How did you show the amount of time you spend on each activity?” (In hours, in minutes, as intervals of time—for example: 8:30 to 3:30)
 “Let’s look at how Mai spends her day in hours and minutes.”
Activity
 7–8 minutes: independent work time
 2–3 minutes: partner discussion
 Monitor for the ways students convert large numbers of hours and fractional hours into minutes.
Student Facing
The table shows how Mai spends the time she is awake on a school day.
activity  hours  minutes 

morning routine  1  
getting to school  \(\frac{1}{2}\)  
time at school  8  
getting home from school  \(\frac{3}{4}\)  
homework and reading  \(1\frac{1}{2}\)  
playing and family time  2  
bedtime routine  \(\frac{1}{4}\) 

Complete the table to show how many minutes Mai spends on each activity. Be prepared to explain or show your reasoning.
 How many hours does Mai spend at school? How many minutes is that? Explain or show how you know.
 How many minutes does Mai sleep on a school night? Explain or show your reasoning.
Student Response
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Activity Synthesis
 Invite selected students to share their responses and reasoning. Start with students who reason additively about the number of minutes in a given number of hours. End with those who frame the relationship between a whole number of hours and the number of minutes in multiplicative terms.
Activity 2: Precious Minutes and Seconds (15 minutes)
Narrative
In this activity, students reason about the number of seconds in given time in minutes. Students see that 1 minute is 60 times as long as 1 second.
Supports accessibility for: Memory, SocialEmotional Functioning
Launch
 Groups of 2
 “Have you used a timer or a stopwatch to count the number of seconds of doing something? What were you timing?”
 Consider challenging students to do something for a full minute (for instance, holding breath or balancing on one foot) and displaying a timer that shows the second hand or the number of seconds increasing or decreasing.
 “Which one is longer: 1 minute or 1 second? How does 1 minute compare to 1 second?” (One minute is 60 times as long as 1 second.)
Activity
 7–8 minutes: independent work time
 2–3 minutes: partner discussion
 Monitor for the different ways students find the number of seconds in 10 and 30 minutes and the ways they reason about the last 2 problems.
Student Facing
Diego set a timer to make sure that things are not done for too long or too short an amount of time.
activity  minutes  seconds 

brushing teeth  2  
showering  3  
heating a cup of milk in the microwave  \(\frac{1}{2}\)  
break during homework time  5  
quick workout  10  
daily reading  30 
 Complete the table with the number of seconds for each activity. Be prepared to explain your reasoning.

Diego noticed that on a television channel, commercial breaks are often between \(1\frac{1}{2}\) and \(2\frac{1}{2}\) minutes long each. How long are they in seconds? Explain or show your reasoning.

Diego’s workout starts with 4 minutes of warmup and stretching, followed by 100 seconds of jumping jacks.
If he works out for 10 minutes exactly, how many more seconds are left in his workout?
Student Response
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Activity Synthesis
 Display the table. Invite students to help complete the table by sharing their responses and reasoning.
 “How did you find the number of seconds in 30 minutes?” (Multiply the number of seconds in 10 minutes by 3, multiply the number seconds in 5 minutes by 6.)
 Select other students to share their reasoning for the problem about commercial breaks.
 Highlight that we can decompose the number of minutes to find the number of seconds. (For example, \(1\frac{1}{2}\) minutes is 1 minute and \(\frac{1}{2}\) minute or 1 minute and 30 seconds, which is 90 seconds.)
Lesson Synthesis
Lesson Synthesis
“Today we used hours, minutes, and seconds to express lengths of time. We converted hours to minutes and then minutes to seconds.”
Display two tables as shown.
hours  minutes 

1  
5  
10 
minutes  seconds 

1  
5  
10 
“If someone claims that the missing numbers in the first table are the same as the ones in the second table, would you agree? Why or why not?” (Agree. An hour is 60 minutes or 60 times as long as 1 minute, and a minute is 60 seconds or 60 times as long as 1 second. The relationship between hour and minutes is the same as that between minute and seconds.)
Complete the table as a class.
Consider asking, “How can we use the information in the tables to help us find the number of seconds in 1 hour?”
Cooldown: Time on Chores (5 minutes)
CoolDown
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