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Time intervals Knowledge-Based Study

Math · Measurement · Math · Time & Money

Math topic explanations on Time intervals.

Study notes

  1. What Is a Time Interval?

    A time interval, also known as elapsed time, is the amount of time that passes from the start of an event to its end.

    Every time interval involves three key components:

    • Start time: The moment an event begins.
    • End time: The moment an event finishes.
    • Elapsed time (interval): The duration between the start time and the end time.

    Time intervals are typically measured in seconds, minutes, and hours, where:

    • 1 minute = 60 seconds
    • 1 hour = 60 minutes
    • 1 day = 24 hours

    Finding the Duration

    To find the time interval between two given times, you calculate how much time has passed. A reliable method is to break the calculation into benchmark steps using an open number line or mental jumps.

    Example: Within the Same Day

    A train departs at 08:25 and arrives at 11:10. What is the length of the journey?

    1. Jump to the next full hour: From 08:25 to 09:00 is 35 minutes.
    2. Jump across full hours: From 09:00 to 11:00 is 2 hours.
    3. Jump to the end time: From 11:00 to 11:10 is 10 minutes.
    4. Combine the intervals: 2 hours + 35 minutes + 10 minutes = 2 hours and 45 minutes.

    Tip: Always convert minutes exceeding 60 into additional hours. For example, 75 minutes is equal to 1 hour and 15 minutes.

    Working Forwards and Backwards

    When the duration is known along with either the start time or the end time, you can find the missing time by adding or subtracting the interval.

    Finding the End Time

    To find an end time, add the interval to the start time.

    Example: A film starts at 14:40 and lasts 1 hour and 35 minutes.

    • Add 1 hour: 14:40 + 1 hour = 15:40
    • Add the remaining 35 minutes: 15:40 + 20 minutes = 16:00, then 16:00 + 15 minutes = 16:15.

    Finding the Start Time

    To find a start time, subtract the interval from the end time by working backwards.

    Example: A cake finishes baking at 13:05 after baking for 45 minutes.

    • Subtract 5 minutes to reach the hour: 13:05 - 5 minutes = 13:00
    • Subtract the remaining 40 minutes: 13:00 - 40 minutes = 12:20.

    Handling 12-Hour and 24-Hour Formats

    When working with 12-hour time, pay close attention to transitions between a.m. and p.m. Midday (12:00 p.m.) and midnight (12:00 a.m.) are critical boundary points.

    Example: Crossing Midday

    A science workshop begins at 10:45 a.m. and concludes at 1:20 p.m.

    • From 10:45 a.m. to 12:00 p.m. (noon): 1 hour and 15 minutes.
    • From 12:00 p.m. to 1:20 p.m.: 1 hour and 20 minutes.
    • Total interval: (1 hour + 1 hour) + (15 minutes + 20 minutes) = 2 hours and 35 minutes.

    Using 24-hour time can simplify calculations across midday because the hours progress continuously from 00:00 to 23:59 without changing notation.