seegongsik
Grade 3 (age 8-9)

grade 3 Time Calculation

On a clock, the short hand points to the hour and the long hand to the minutes. We work with time every day, like figuring out when a movie ends or how long homework took. To find elapsed time, subtract the start time from the end time, and if there aren't enough minutes, trade 1 hour for 60 minutes. Read the time on the clock above, then set a start time and an end time below to see right away how many hours and minutes passed in between.

Reading a clock

🕒 Reading the hour and minute hands
①The last number the short hand (hour hand) has passed is the hour
②Each small mark the long hand (minute hand) points to is 1 minute, and each number is 5 minutes
③When the minute hand points to 12, it is exactly on the hour
④The green numbers under the clock show the time
3
30

Finding elapsed time

9
15
11
40
⏱️ How to find elapsed time
①Subtract the start time from the end time
②Subtract minutes from minutes and hours from hours
③If there aren't enough minutes, trade 1 hour for 60 minutes
④The gold text between the start (blue) and the end (green) shows the elapsed time
⑤Hours go from 1 to 12, so if the end time is earlier than the start, it counts as having passed 12 o'clock once

Wrap-up

Units of time
1 hour = 60 minutes, 1 minute = 60 seconds
Every 60 of a time unit makes 1 of the next unit up
Elapsed time
elapsed time = end time − start time
The difference between two times is the elapsed time
Regrouping time
2:10 − 1:30 → 1 h 70 min − 1 h 30 min = 40 min
If there aren't enough minutes, trade 1 hour for 60 minutes
🎯 Remember
①1 hour is 60 minutes, and 1 minute is 60 seconds
②The short hand shows the hour, and the long hand shows the minutes
③Elapsed time is the end time minus the start time
④If there aren't enough minutes, borrow 60 minutes from the hours
⑤A day is 24 hours, or 1440 minutes

Examples and unit check

Example 1
A movie starts at 2:20 and ends at 4:00. How long is the movie?
1
Subtract the start time from the end time. Set the start to 2:20 and the end to 4:00 in the picture above to see the same answer.
2
In 4:00 − 2:20 there aren't enough minutes, so trade 1 hour for 60 minutes: 3 h 60 min − 2 h 20 min = 1 hour 40 minutes.
▸ 1 hour 40 minutes
If you know the start and end times, you can find how long it took.
Example 2
You start homework at 3:50 and finish at 4:30. How long did it take?
1
Subtract the start time from the end time. There aren't enough minutes, so trade 1 hour for 60 minutes.
2
4:30 becomes 3 h 90 min. 90 − 50 = 40 minutes and 3 − 3 = 0 hours, so it took 40 minutes.
▸ 40 minutes
If there aren't enough minutes, borrow 1 hour (60 minutes) from the hours.
Unit check
How many minutes are there in 2 hours 30 minutes?
①150 min
②230 min
③90 min
④120 min
▸ ① 150 min
1
2 hours = 2 × 60 = 120 minutes.
2
120 minutes + 30 minutes = 150 minutes.
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Finding Patterns

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