Solved Exercises on Elapsed Time Practice in Grade 3

Master elapsed time calculations: calculating time intervals, solving word problems, and understanding time duration through these 3 detailed exercises.

Solution: Exercises 1 to 3
1 Basic elapsed time
Exercise 1
Sarah started reading at 2:15 PM and finished at 3:45 PM. How long did she read?
Definition:

Elapsed time: The amount of time that passes between two events

Elapsed time method:
  1. Identify the start and end times
  2. Count the full hours between times
  3. Count the remaining minutes
  4. Add the hours and minutes together
Start Time
2:15 PM
End Time
3:45 PM
Elapsed Time
1 hour 30 minutes
Start
2:15 PM
→
End
3:45 PM
Step 1: Identify start and end times

Start time: 2:15 PM, End time: 3:45 PM

Step 2: Count the full hours

From 2:15 PM to 3:15 PM = 1 full hour

Step 3: Count the remaining minutes

From 3:15 PM to 3:45 PM = 30 minutes

Step 4: Add hours and minutes

1 hour + 30 minutes = 1 hour 30 minutes

Sarah read for 1 hour 30 minutes
Final answer:

Sarah read for 1 hour 30 minutes

Applied rules:

• Time counting: Count full hours first, then remaining minutes

• Subtraction: Calculate the difference between times

• Conversion: Express time in hours and minutes format

Start
2:15 PM
→ 1h 30m →
End
3:45 PM
2 Word problem with elapsed time
Exercise 2
A movie starts at 6:30 PM and lasts for 2 hours and 15 minutes. What time does it end?
Definition:

End time calculation: Start time + Duration = End time

Start Time
6:30 PM
Duration
2h 15m
End Time
8:45 PM
Start
6:30 PM
+ 2h 15m →
End
8:45 PM
Step 1: Identify start time and duration

Start time: 6:30 PM, Duration: 2 hours 15 minutes

Step 2: Add hours to start time

6:30 PM + 2 hours = 8:30 PM

Step 3: Add remaining minutes

8:30 PM + 15 minutes = 8:45 PM

Step 4: State the final time

The movie ends at 8:45 PM

The movie ends at 8:45 PM
Final answer:

The movie ends at 8:45 PM

Applied rules:

• Addition: Start time + Duration = End time

• Carry over: If minutes exceed 60, convert to next hour

• Time format: Maintain proper AM/PM notation

Start
6:30 PM
+ 2h 15m →
End
8:45 PM
3 Elapsed time across hours
Exercise 3
Emma started her homework at 4:45 PM and finished at 6:20 PM. How long did she work on her homework?
Definition:

Cross-hour elapsed time: Time that spans across multiple hours

Start Time
4:45 PM
End Time
6:20 PM
Elapsed Time
1h 35m
Start
4:45 PM
→
End
6:20 PM
Step 1: Identify start and end times

Start time: 4:45 PM, End time: 6:20 PM

Step 2: Count from start time to next full hour

From 4:45 PM to 5:00 PM = 15 minutes

Step 3: Count the full hours

From 5:00 PM to 6:00 PM = 1 hour

Step 4: Count from full hour to end time

From 6:00 PM to 6:20 PM = 20 minutes

Step 5: Add all time segments

15 minutes + 1 hour + 20 minutes = 1 hour 35 minutes

Emma worked on her homework for 1 hour 35 minutes
Final answer:

Emma worked on her homework for 1 hour 35 minutes

Applied rules:

• Segmentation: Break time into manageable segments

• Counting: Count up to next hour, then continue

• Aggregation: Combine all time segments for total

Start
4:45 PM
→ 1h 35m →
End
6:20 PM
Rules and methods, laws,...
End Time - Start Time = Elapsed Time
Elapsed Time Formula
Rule 1
Start + Duration = End
Finding End Time
Rule 2
End - Start = Duration
Finding Elapsed Time
Rule 3
End - Duration = Start
Finding Start Time
Key definitions:

Elapsed time: The amount of time that passes between two events

Start time: When an event begins

End time: When an event finishes

Duration: How long an event lasts

Complete methodology:
  1. Identify the problem: Determine if finding elapsed time, start time, or end time
  2. Choose the method: Count up, count down, or use time lines
  3. Calculate: Use appropriate time calculation technique
  4. Verify: Check if the answer makes sense
Tip 1: Draw a number line to visualize the passage of time.
Tip 2: Count up to the next hour, then continue counting.
Tip 3: Remember that there are 60 minutes in an hour.
Tip 4: Use analog clocks to visualize time passage.
Common errors: Forgetting to carry over minutes to hours, miscounting across hour boundaries.
Practice tips: Use real-life scenarios, practice with clock manipulatives, create time stories.
Formulas to know by heart:

• Elapsed Time = End Time - Start Time

• End Time = Start Time + Duration

• Start Time = End Time - Duration

• 1 hour = 60 minutes

Key Concepts and Practice Tips
Time = Hours + Minutes
Time Format
Time Measurement Units:

Seconds: The smallest unit of time (60 seconds = 1 minute)

Minutes: Medium unit of time (60 minutes = 1 hour)

Hours: Larger unit of time (24 hours = 1 day)

Time Calculation Strategies:
  1. Counting Up Method: Start at the beginning time and count forward
  2. Counting Down Method: Start at the end time and count backward
  3. Breaking Into Parts: Split time into hours and minutes separately
  4. Using Number Lines: Visual representation of time passage
Visualization Tip: Imagine the hands of a clock moving to see elapsed time.
Chunking Strategy: Break large time intervals into smaller chunks.
Estimation: Estimate the answer first, then calculate precisely.
Verification: Add your answer to the start time to check.
Real-world applications: Schedule planning, cooking, travel time, sports timing.
Problem-solving steps: Read, identify, plan, solve, check, answer.
Important Time Facts:

• 1 minute = 60 seconds

• 1 hour = 60 minutes = 3,600 seconds

• 1 day = 24 hours = 1,440 minutes

• AM = Ante Meridiem (before noon)

• PM = Post Meridiem (after noon)

Additional Practice Problems and Solutions
Practice Makes Perfect!
More Examples
Additional Practice Problems:

Problem 1: If lunch starts at 12:10 PM and ends at 1:05 PM, how long is lunch?

Problem 2: A soccer game lasted 1 hour and 45 minutes. If it ended at 4:30 PM, when did it start?

Problem 3: How much time passes from 9:25 AM to 11:15 AM?

Solution Approaches:

For Problem 1: From 12:10 PM to 1:05 PM

Step 1: From 12:10 PM to 1:00 PM = 50 minutes

Step 2: From 1:00 PM to 1:05 PM = 5 minutes

Step 3: Total = 50 + 5 = 55 minutes

For Problem 2: Working backwards from 4:30 PM - 1 hour 45 minutes

Step 1: 4:30 PM - 1 hour = 3:30 PM

Step 2: 3:30 PM - 45 minutes = 2:45 PM

For Problem 3: From 9:25 AM to 11:15 AM

Step 1: From 9:25 AM to 10:00 AM = 35 minutes

Step 2: From 10:00 AM to 11:00 AM = 1 hour

Step 3: From 11:00 AM to 11:15 AM = 15 minutes

Step 4: Total = 1 hour + 35 minutes + 15 minutes = 1 hour 50 minutes

Strategy 1: Always identify whether you're finding elapsed time, start time, or end time.
Strategy 2: When subtracting times, it may help to break the problem into parts.
Strategy 3: Use the relationship: Start + Elapsed = End or End - Start = Elapsed.
Strategy 4: Draw a timeline when problems seem complex.
Memory aids: "Time flies!" - Remember that time moves forward consistently.
Checking answers: Add your elapsed time to the start time to verify the end time.
Key Takeaways:

• Elapsed time is the difference between two times

• Count hours first, then minutes

• Use benchmarks like the next full hour to make calculations easier

• Always express answers in hours and minutes when appropriate

• Check your work by adding the elapsed time back to the start time

Questions & Answers

Question: I get confused when calculating elapsed time that goes past the hour. For example, from 3:45 to 4:20. Can you explain how to handle this?

Answer: Great question! When elapsed time crosses an hour boundary, break it into parts:

  • First, count from your start time to the next full hour: From 3:45 to 4:00 = 15 minutes
  • Then, count from the full hour to your end time: From 4:00 to 4:20 = 20 minutes
  • Finally, add the two parts together: 15 minutes + 20 minutes = 35 minutes

This strategy makes the problem easier because you're only dealing with minutes in each part. Using round numbers (like full hours) as benchmarks helps simplify the calculation.

Visual tip: Think of it as taking two smaller jumps instead of one big jump across the hour boundary!

Question: When do I need to convert minutes to hours in my answer? How do I know when to do this?

Answer: You should convert minutes to hours when you have 60 or more minutes in your answer:

  • If you have 60 minutes, that equals 1 hour
  • If you have 120 minutes, that equals 2 hours
  • If you have 75 minutes, that equals 1 hour and 15 minutes

The rule is: every 60 minutes = 1 hour. So divide the total minutes by 60 to find how many whole hours there are, and the remainder will be the extra minutes.

Example: If you calculate 135 minutes, divide 135 ÷ 60 = 2 with remainder 15, so the answer is 2 hours and 15 minutes.

Question: How can I help my child understand elapsed time better? Are there any fun activities we can do together?

Answer: Here are some engaging activities to reinforce elapsed time concepts:

  • Create a daily schedule and calculate how long activities take
  • Use a real clock to practice moving hands and seeing time pass
  • Play "How Long Ago?" games - ask questions like "What time was it 30 minutes ago?"
  • Cook together and calculate cooking times for different dishes
  • Plan a pretend trip and calculate travel times between destinations

Make it visual: Draw timelines, use manipulative clocks, or even use a timer to physically experience the passage of time. Real-world connections make abstract concepts more concrete!