# Into Math Grade 4 Module 21 Lesson 3 Answer Key Solve Problems Involving Start Time and End Time

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## HMH Into Math Grade 4 Module 21 Lesson 3 Answer Key Solve Problems Involving Start Time and End Time

I Can use visual models to represent, add, and subtract times to solve problems involving start and end times.

Step It Out

Question 1.
Annabelle’s softball game lasted 2 hours 30 minutes. The game ended at 1:30 p.m. At what time did the game start?

A. What information do you know?
I know the game ended time is 1:30 p.m. and game lasted time 2 hours 30 minutes.

B. What information do you need to know?
I need to know the start time of the Annabelle’s softball game.

C. Use a number line to help you find what you need. Show time jumps on the number line below.

D. At what time did Annabelle’s softball game start?
Annabelle’s softball game start at 11:00 a.m.

Turn and Talk What other strategy could you use to solve the problem?
The other strategy you can use to solve the problem is addition.

Question 2.
Nakai’s basketball game starts at 6:50 p.m. and lasts 2 hours 15 minutes. At what time does the game end?

A. How can you regroup minutes and seconds?
Minutes and seconds are regrouped as follows.
1 hour is equal to 60 minutes.
1 minute is equal to 60 seconds.

B. Use addition to find the end time.

• First, add the minutes to the start time.
• Last, regroup the minutes as hours.

Explanation:
Given start time is 6 hours 50 minutes and elapsed time is 2 hours 15 minutes. First, we have to add the minutes to the start time. Next, we have to add the hours. Add 6 hours 50 minutes with 2 hours 50 minutes the sum is equal to 8 hours 65 minutes. Here, we have to regroup the minutes as hours. We know that 1 hour is equal to 60 minutes. The time 8 hours 65 minutes is regrouped as 9 hours 5 minutes. So, the end time is 9:05 p.m.

C. At what time does Nakai’s basketball game end?
Nakai’s basketball game ends at 9:05 p.m.

Question 3.
The third chess match of the day ended at 3:48:16 p.m. What time did the third chess match start?

A. Use subtraction to find the start time.

• First, subtract the minutes to the start time.
• Next, subtract the hours.
• Last, subtract as hours.

Explanation:
The third chess match of the day ended at 3:48:16 p.m. The elapsed time is 17 minutes 27 seconds. First we have to subtract the seconds. Next, we have to subtract the minutes and last subtract hours. Here 27 seconds is greater than 16 seconds. Regroup 1 minutes as 60 seconds. So, the end time 3 hours 48 minutes 16 seconds is regrouped as 3 hours 47 minutes 76 seconds. Subtract the elapsed time from end time the difference is equal to 3 hours 30 minutes 49 seconds. So, the start time is equal to 3:30:49 p.m.
B. What time did the third chess match start?
The third chess match start at 3:30:49 p.m.

Turn and Talk How does finding the start time compare to finding the end time?
The start time is calculated by subtracting the elapsed time from end time.
The end time is calculated by adding the start time with elapsed time.

Check Understanding

Question 1.
Kate’s hockey game lasts 2 hours 30 minutes and ends at 6:45 p.m. At what time does her game start? Use a number line.

Start time: _______

Kate’s hockey game starts at 4:15 p.m.
Explanation:
Kate’s hockey game lasts 2 hours 30 minutes and ends at 6:45 p.m. The time difference between 6:45 to 6:15 is 30 minutes and 6:15 to 5:15 is 1 hour and 5:15 to 4:15 is 1 hour. By adding all the time differences the elapsed time is equal to 2 hours 30 minutes as we can observe in the above number line. So, Kate’s hockey game starts at 4:15 p.m.

Question 2.
Jordon starts working on an art project at 3:55 p.m. and spends 3 hours 25 minutes working on it. At what time does he stop?
Jordon starts working on an art project at 3:55 p.m. and spends 3 hours 25 minutes working on it. Here we have to calculate the end time. To calculate end time we need to perform addition operation. Add start time with elapsed time. First we have to add minutes and add hours.
3 hours 55 minutes + 3 hours 25 minutes = 6 hours 80 minutes
Regroup 1 hour as 60 minutes.
The end time 6 hours 80 minutes is regrouped as 7 hours 20 minutes.
Jordon stops working on an art project at 7:20 p.m.

Question 3.
Jesse needs to be at track practice at 2:45 p.m. It takes him 20 minutes to walk to the track from his home. At what time should he leave his home? Solve using a strategy of your choice.
Jesse needs to be at track practice at 2:45 p.m. It takes him 20 minutes to walk to the track from his home.
End time = 2:45 p.m.
Elapsed time = 20 minutes
Start time = ?
To calculate start time we need to perform subtraction operation. Subtract elapsed time from end time. First we have to subtract minutes next hours.
2 hours 45 minutes – 20 minutes = 2 hours 25 minutes
Jesse need to leave his home at 2:25 p.m.

Question 4.
Open Ended Write and solve a problem involving a start time or an end time using an elapsed time of 4 hours 10 minutes.
Last Sunday, John’s family went to Zoo park where they started from their home at 8:20 a.m. The elapsed time to return back to their home is 4 hours 10 minutes. What is the time they returned home?
Start time = 8:20 a.m.
Elapsed time = 4 hours 10 minutes
End time = ?
To calculate end time we need to perform addition operation. Add start time with elapsed time. First we have to add minutes and next add hours.
8 hours 20 minutes + 4 hours 10 minutes = 12 hours 30 minutes
The end time is 12:30 p.m.
John’s family returned home at 12:30 p.m.

Question 5.
Music Symphony No. 5 is a piece of music written over 200 years ago by famous composer Ludwig van Beethoven. An orchestra plays Symphony No. 5 for 33 minutes 28 seconds. If they start at 6:47:15 p.m., what time will the orchestra finish playing Symphony No. 5?

An orchestra plays Symphony No. 5 for 33 minutes 28 seconds. They start at 6:47:15 p.m.
Start time = 6:47:15 p.m.
Elapsed time = 33 minutes 28 seconds
End time = ?
To calculate end time we need to perform addition operation. Add start time with elapsed time. First we have to add seconds next add minutes and last add hours.
6 hours 47 minutes 15 seconds + 33 minutes 28 seconds = 6 hours 80 minutes 43 seconds
Here, we have to regroup the minutes as hours. We know that 1 hour is equal to 60 minutes. The time 6 hours 80 minutes 43 seconds is regrouped as 7 hours 20 minutes 43 seconds. So, the end time is 7:20:43 p.m.
The orchestra finishes playing Symphony No. 5 at 7:20:43 p.m.

Question 6.
Attend to Precision The W Train left Village Park Station and arrived at Central Station at 8:15:15 a.m. The train traveled for 1 hour 35 minutes 5 seconds. At what time did the W Train leave Village Park Station?

The W Train left Village Park Station and arrived at Central Station at 8:15:15 a.m. The train traveled for 1 hour 35 minutes 5 seconds.
End time = 8:15:15 a.m.
Elapsed time = 1 hour 35 minutes 5 seconds
Start time = ?
To calculate start time we need to perform subtraction operation. Subtract elapsed time from end time. First we have to subtract seconds, next subtract minutes and last subtract hours.
Here 34 minutes is greater than 15 minutes. Here, we have to regroup the minutes as hours. We know that 1 hour is equal to 60 minutes. So, the end time 8 hours 15 minutes 15 seconds is regrouped as 7 hours 75 minutes 15 seconds.
7 hours 75 minutes 15 seconds – 1 hour 35 minutes 5 seconds = 6 hours 40 minutes 10 seconds
The W Train leaves Village Park Station at 6:40:10 a.m.

Question 7.
Farha starts her science homework at 3:30 p.m. She works for 35 minutes, takes a 20 minute break to eat her snack, and then starts working on her science homework again. At what time does she start working on her science homework again?
Farha starts her science homework at 3:30 p.m. She works for 35 minutes.
Add 3 hours 30 minutes with 35 minutes the sum is equal to 3 hours 65 minutes.
Here, we have to regroup the minutes as hours. We know that 1 hour is equal to 60 minutes.
The time 3 hours 65 minutes is regrouped as 4 hours 5 minutes.
Farha takes a 20 minute break to eat her snack, and then starts working on her science homework again.
Add break time 20 minutes to 4 hours 5 minutes the sum is equal to 4 hours 25 minutes.
Farha starts working on her science homework again at 4:25p.m.

Question 8.
Use Tools Ms. Wong drove for 4 hours 24 minutes. She arrived at her sister’s home at 5:12 p.m. At what time did she start driving? Use a number line to solve.

1 hour + 1 hour + 1 hour + 1 hour + 12 minutes + 12 minutes = 4 hours 24 minutes
She starts driving at 12:48 p.m.

Question 9.
A playlist of Ari’s favorite songs has a runtime of 2 hours 23 minutes 57 seconds. If she starts the playlist at 7:42:16 a.m., at what time will it have played all the songs?