# Into Math Grade 4 Module 21 Lesson 2 Answer Key Solve Problems Involving Elapsed Time

We included HMH Into Math Grade 4 Answer Key PDF Module 21 Lesson 2 Solve Problems Involving Elapsed Time to make students experts in learning maths.

## HMH Into Math Grade 4 Module 21 Lesson 2 Answer Key Solve Problems Involving Elapsed Time

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

Step It Out

Question 1.
Alec arrives at the jump rope club meeting at 3:15 p.m. He leaves at 4:05 p.m. How many minutes is Alec at the meeting? A. What information do you know?
I know the start time is 3:15 p.m. and end time is 4:05 p.m.

B. What information do you need to know?
I need to know the elapsed time of Alec at the meeting.

C. Start at 3:15 and count on to 4:05.
Show time jumps on the number line below.  D. How can you find the elapsed time?
________________
How many minutes is Alec at the meeting?
The given start time is 3:15 p.m. and the the end time is 4:05 p.m. The time difference between 3:15 p.m. and 3:30 p.m. is 15 minutes and 3:30 p.m. to 4:00 p.m. is 30 minutes and 4:00 p.m. to 4:05 p.m. is 5 minutes. Add 15 minutes with 30 minutes and 5 minutes the sum is equal to 50 minutes. So, the elapsed time is 50 minutes. Alec stayed 50 minutes at the meeting.

Turn and Talk What is another way you could solve the problem?
Answer: Another strategy you can use to solve the problem is subtraction.

Question 2.
Mrs. Bates rides the bus to the community center. She gets on the bus at 7:36 a.m. and gets off the bus at 8:07 a.m. How long is she on the bus? A. Use the terms elapsed time, start time, and end time to write a subtraction equation that could be used to find elapsed time. Then subtract.  B. How long is Mrs. Bates on the bus?
Mrs. Bates stayed 31 minutes on the bus.

Question 3.
Jill finishes a race at 9:06:48 a.m. The race starts at 6:44:52 a.m. How long does it take Jill to finish the race?
A. How can you use the information you know to find the elapsed time from start to finish?
Jill starts the race at 6:44:52 a.m. and finishes the race at 9:06:48 a.m.
To calculate the elapsed time I will subtract start time from end time.
Elapsed time = End time – Start time

B. Solve.
Start time = 6:44:52 a.m.
End time = 9:06:48 a.m.
Elapsed time = End time – Start time
Elapsed time = 9:06:48 a.m. – 6:44:52 a.m.
Here, First we have to subtract the seconds. Second we have to subtract minutes. Third we have to subtract hours.
Here 44 minutes is greater than 6 minutes and 52 seconds is greater than 48 seconds. Regroup 1 hours as 60 mins and 1 minutes as 60 seconds. So end time 9:06:48 a.m. is regrouped as 8:65:108 a.m.
Elapsed time = 8:65:108 – 6:44:52
Elapsed time = 2:21:56
Jill took 2 hours 21 minutes 56 seconds to finish the race.

Turn and Talk How is regrouping hours and minutes similar to and different from regrouping hundreds, tens, and ones?

Check Understanding

Question 1.
Lunch break starts at 11:10 a.m. and ends at 11:48 a.m. Use the number line to find the elapsed time. Elapsed time: _________ Elapsed time: 38 minutes
Explanation:
The given start time is 11:10 a.m. and the the end time is 11:48 a.m. The time difference between 11:10 a.m. and 11:30 a.m. is 20 minutes and 11:30 a.m. to 11:45 a.m. is 15 minutes and 11:45 a.m. to 11:48 a.m. is 3 minutes. Add 20 minutes with 15 minutes and 3 minutes the sum is equal to 38 minutes. So, the elapsed time is 38 minutes.

Question 2.
Hiroshi times his exercise for the day. He starts walking at 4:18:13 p.m. He stops walking at 4:36:26 p.m. How long does Hiroshi walk?
Hiroshi starts walking at 4:18:13 p.m. and stops walking at 4:36:26 p.m.
Start time = 4:18:13 p.m.
End time = 4:36:26 p.m.
Elapsed time = End time – Start time
= 4:36:26 p.m. – 4:18:13 p.m.
Her, First we have to subtract the seconds. Second we have to subtract minutes. Third we have to subtract hours.
= 0:18:13
Hiroshi walk for 18 minutes 13 seconds.

Find the elapsed time using a strategy of your choice.

Question 3.
Start at 9:45 a.m. End at 11:20 am.
Given start time is 9:45 a.m. and end time is 11:20 a.m.
To calculate elapsed we need to perform subtraction operation. Subtract start time form end time.
Elapsed time = End time – Start time
= 11:20 a.m. – 9:45 a.m.
Here, First we have to subtract the minutes. Next we have to subtract hours.
Here 45 minutes is greater than 20 minutes. Regroup 1 hours as 60 mins. So end time 11:20 a.m. is regrouped as 10:80 a.m.
Elapsed time = 10:80 a.m. – 9:45 a.m.
= 1:35
The elapsed time is 1 hour 35 minutes.

Question 4.
Start at 1:30 p.m. End at 2:16 p.m.
The elapsed time is 46 minutes.
Explanation:
The amount of time that passes between two given time stamps(Start time and End time) is called as elapsed time.
The given start time is 1:30 p.m. and the the end time is 2:16 p.m. The time difference between 1:30 p.m. and 2:00 p.m. is 30 minutes and 2:00 p.m. to 2:16 a.m. is 16 minutes. Add 30 minutes with 16 minutes the sum is equal to 46 minutes. So, the elapsed time is 46 minutes.

Question 5.
Attend to Precision A skier is competing in a cross-country ski competition. He starts the race at 7:05:10 a.m. He crosses the finish line at 9:31:03 a.m. How long does ¡t take him to finish the race? A skier starts the race at 7:05:10 a.m. He crosses the finish line at 9:31:03 a.m.
Elapsed time = End time – Start time
Elapsed time = 9:31:03 a.m. – 7:05:10 a.m.
Here, First we have to subtract the seconds. Second we have to subtract minutes. Third we have to subtract hours.
Here 10 seconds is greater than 3 seconds. Regroup 1 minute as 60 seconds. So end time 9:31:03 a.m. is regrouped as 9:30:63 a.m.
Elapsed time = 9:30:63 a.m.- 7:05:10 a.m.
Elapsed time = 2:25:53
The elapsed time is 2 hours 25 minutes 53 seconds.
He took 2 hours 25 minutes 53 seconds to finish the race.

Question 6.
Attend to Precision A play starts at 9:10 a.m. and ends at 10:52 a.m. Show how to find the elapsed time.
How long is the play?
The elapsed time is 42 minutes.
Explanation:
The amount of time that passes between two given time stamps(Start time and End time) is called as elapsed time.
The given start time is 9:10 a.m. and the the end time is 10:52 a.m. The time difference between 9:10 a.m. and 9:30 a.m. is 20 minutes and 9:30 a.m. to 10:52 a.m. is 22 minutes. Add 20 minutes with 22 minutes the sum is equal to 42 minutes. So, the elapsed time is 42 minutes. The play is 42 minutes.

Question 7.
Critique Reasoning Harold solved the following problem incorrectly. This shows Harold’s solution. Explain his error, and show the correct solution. Soccer practice started at 3:55 p.m. Practice finished at 5:35 p.m. How long did soccer practice take?
Harold error is he didn’t regrouped the hours. He directly subtracted the given times.
Soccer practice started at 3:55 p.m. Practice finished at 5:35 p.m.
To calculate elapsed we need to perform subtraction operation. Subtract start time form end time.
Elapsed time = End time – Start time
= 5:35 p.m. – 3:55 p.m.
Here, First we have to subtract the minutes. Next we have to subtract hours.
Here 55 minutes is greater than 35 minutes. Regroup 1 hours as 60 mins. So end time 5:35 p.m. is regrouped as 4:95 p.m.
Elapsed time = 4:95 p.m. – 3:55 a.m.
= 1:40
The elapsed time is 1 hour 40 minutes.
Soccer practice took 1 hour 40 minutes.

Question 8.
Reason Amare and Gabriella are waiting at the airport. Amare’s flight was scheduled to depart at 4:30 p.m. but is delayed until 5:48 p.m. Gabriella’s flight was scheduled to depart at 5:36 p.m but is delayed until 6:15 p.m. Amare says that his flight was delayed twice as long as Gabriella’s flight. Is he correct? Explain. 