Grade 4
  1. Numbers and Place Value  1.1. Understanding Place Value  1.2. Reading and Writing Large Numbers  1.3. Comparing and Ordering Numbers  1.4. Rounding Numbers  1.5. Understanding Odd and Even Numbers  1.6. Number Patterns and Sequences
  2. Addition and Subtraction  2.1. Addition of Large Numbers  2.2. Subtraction of Large Numbers  2.3. Estimation in Addition and Subtraction  2.4. Word Problems on Addition and Subtraction
  3. Multiplication and Division  3.1. Understanding Multiplication  3.2. Multiplying Multi-Digit Numbers  3.3. Understanding Division  3.4. Dividing Multi-Digit Numbers  3.5. Multiplication and Division Facts  3.6. Word Problems on Multiplication and Division
  4. Factors and Multiples  4.1. Understanding Factors  4.2. Finding Common Factors  4.3. Understanding Multiples  4.4. Finding Common Multiples  4.5. Prime and Composite Numbers  4.6. Prime Factorization  4.7. Greatest Common Factor  4.8. Least Common Multiple
  5. Fractions  5.1. Understanding Fractions  5.2. Equivalent Fractions  5.3. Simplifying Fractions  5.4. Comparing and Ordering Fractions  5.5. Addition of Fractions  5.6. Subtraction of Fractions  5.7. Mixed Numbers and Improper Fractions  5.8. Converting Mixed Numbers to Improper Fractions  5.9. Word Problems on Fractions
  6. Decimals  6.1. Understanding Decimals  6.2. Reading and Writing Decimals  6.3. Comparing and Ordering Decimals  6.4. Rounding Decimals  6.5. Addition of Decimals  6.6. Subtraction of Decimals  6.7. Converting Decimals to Fractions  6.8. Converting Fractions to Decimals  6.9. Word Problems on Decimals
  7. Measurement  7.1. Length  7.1.1. Units of Length  7.1.2. Converting Units of Length  7.1.3. Perimeter  7.1.4. Area  7.1.5. Word Problems on Length  7.2. Weight  7.2.1. Units of Weight  7.2.2. Converting Units of Weight  7.2.3. Word Problems on Weight  7.3. Volume and Capacity  7.3.1. Units of Volume  7.3.2. Converting Units of Volume  7.3.3. Estimating Volume and Capacity  7.3.4. Word Problems on Volume and Capacity  7.4. Time  7.4.1. Reading Time  7.4.2. Units of Time  7.4.3. Converting Units of Time  7.4.4. Calculating Elapsed Time  7.4.5. Word Problems on Time
  8. Geometry  8.1. Properties of Shapes  8.1.1. Types of Angles  8.1.2. Types of Triangles  8.1.4. Symmetry  8.1.5. Lines of Symmetry  8.2. Perimeter and Area  8.2.1. Perimeter of Rectangles  8.2.2. Perimeter of Other Shapes  8.2.3. Area of Rectangles  8.2.4. Area of Other Shapes  8.2.5. Area of Irregular Shapes  8.3. Coordinate Geometry  8.3.1. Understanding Coordinates  8.3.2. Plotting Points on a Grid  8.3.3. Identifying Shapes on a Grid
  9. Data and Graphs  9.1. Types of Data  9.2. Organizing Data  9.3. Reading Bar Graphs  9.4. Drawing Bar Graphs  9.5. Line Plots  9.7. Reading and Interpreting Line Graphs  9.8. Word Problems on Graphs
  10. Money  10.1. Understanding Money  10.2. Addition and Subtraction with Money  10.3. Making Change  10.4. Multiplying and Dividing Money  10.5. Word Problems on Money

Grade 4 → Measurement → Time ↓


Calculating Elapsed Time


Understanding how to calculate elapsed time is an important skill in math and everyday life. Elapsed time is the time from the start of an event to the end of an event. Mastering this concept helps in managing schedules, understanding deadlines, and solving real-world problems. In this guide, we will go over the concept of elapsed time step-by-step, providing both text and visual examples to make learning fun and comprehensive.

What is the elapsed time?

Elapsed time is easy to understand. It is the time between the start and the end of an event. For example, if you start watching a movie at 2:30 PM and it ends at 4:00 PM, the movie has lasted 1 hour and 30 minutes. In this case, 1 hour and 30 minutes is the elapsed time.

Units of time measurement

Before we start calculating elapsed time, it will be useful to review the units of time measurement:

  • Second: The basic unit of time.
  • Minute: 1 minute is equal to 60 seconds.
  • Hours: 1 hour is equal to 60 minutes.

Steps to calculate elapsed time

Here are the steps to calculate the time elapsed between two times:

  1. Write down the start and end times.

    For example, if the event starts at 3:15 PM and ends at 6:45 PM, these are your start and end times.

  2. If needed convert both times to 24 hour format for easier calculations.

    Example: 3:15 PM becomes 15:15 and 6:45 PM becomes 18:45.

  3. Divide the time into hours and minutes.
  4. Calculate the difference for hours and minutes separately.

    Subtract the starting hour from the ending hour, and do the same for the minutes.

  5. Combine the hours and minutes to find the total elapsed time.

    Be sure to adjust the minutes to hours when the time exceeds 60 minutes.

Example 1: Simple elapsed time calculation

Let's consider an example where a friend comes to visit you. They arrive at 1:20 PM and leave at 4:00 PM. We want to know how long their visit lasted.

Start time: 1:20 PM
End time: 4:00 PM

To calculate elapsed time:

  1. Minutes: We find the difference in minutes between the end (00 min) and the start (20 min). 
    00 - 20 = -20
    Since we get a negative value, we borrow 1 hour (60 minutes) and calculate the minutes: 
    (60 + 00) – 20 = 40 minutes
  2. Hours: Subtract the initial hour from the last hour, remember we borrowed an hour. 
    3 (from 4) - 1 = 2 hours

Therefore, the time elapsed is 2 hours and 40 minutes.

Start: 1:20 PM End: 4:00 PM Time elapsed: 2 hours 40 minutes

Example 2: Calculating time elapsed overnight

Suppose you start reading a book at 10:15 pm and read till 1:30 am. How much time have you read?

To convert both times to 24-hour format: 

Start time: 22:15
Expiry time: 01:30
Calculate elapsed time:

  1. Minutes: 
    30 (end) - 15 (start) = 15 minutes
  2. Hours: Since the program runs after midnight, we add 24 to the last hour to simplify the calculation: 
    (24 + 1) - 22 = 3 hours

Total elapsed time is 3 hours 15 minutes.

Start: 10:15 PM End: 1:30 AM Elapsed time: 3 hours 15 minutes

Example 3: Elapsed time with AM and PM

Let's calculate the time spent by John starting his homework at 8:45 am and finishing it at 2:17 pm.

Start time: 8:45 am
End time: 2:17 PM

To find the elapsed time:

  1. Convert hours to 24-hour format. 
    Start: 08:45 
End: 14:17
  2. Minutes: 
    17 (end) - 45 (start) = -28 (borrow 1 hour)
(60 + 17) - 45 = 32 minutes
  3. Hours: 
    (14 - 1) - 8 = 5 hours

In total, John spent 5 hours and 32 minutes on his homework.

Start: 8:45 am End: 2:17 PM Elapsed time: 5 hours 32 minutes

Handling special cases

Some situations require attention to detail, such as when the start or end time involves seconds, when the session extends beyond a day, or when events are scheduled in different time zones. Although dealing with these can be more complex, the principles of splitting the calculation into different units and adjusting for overflow remain the same.

Practice problems

Try solving the following problems to strengthen your understanding of the past:

  • Calculate the elapsed time between 9:30 AM and 12:15 PM.
  • If a train departs at 11:55 pm and arrives at 3:20 am, how much time will the journey take?
  • How much time has passed from 6:45 am to 9:10 am?
  • A concert starts at 7:50 pm and ends at 11:30 pm. What is its duration?
  • Determine the elapsed time for a marathon starting at 5:00 AM and ending at 2:45 PM.

Solve these problems step by step, as in the examples above.

Conclusion

Calculating elapsed time is a valuable skill that extends beyond the classroom. It takes practice to master it. By following a structured approach and practicing a variety of problems, you can become proficient at determining elapsed time. Keep practicing, understand each step, and use the tools and strategies discussed here to gain confidence in measuring elapsed time.

Understanding the basics of time measurement and conversion, handling different scenarios with adjustments, and practicing regularly will make calculating elapsed time an easy and routine task.


Grade 4 → 7.4.4


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Calculating Elapsed Time

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