Grade 3 (age 8-9)

Time Calculation

The short hand on a clock shows the hour, and the long hand shows the minutes. We work with time every day, like knowing when a movie ends or how long homework took. To find how much time has passed, subtract the start time from the end time, and if the minutes run short, trade one hour for sixty minutes. Move the sliders to set the hands, then choose a start and end time to work out the hours and minutes in between.

Reading a Clock

🕒 Read the Hour and Minute Hands

①Short hand (hour) points to the hour

②Long hand (minute) points to the minute

③Minute hand on 12 = on the hour

Hour3

Minute30

Finding Elapsed Time

Start Hour9

Start Min15

End Hour11

End Min40

⏱️ How to Find Elapsed Time

①Subtract start time from end time

②Subtract minutes, then hours

③If minutes short, borrow 60 from 1 hour

Summary

Time Units

1 hour = 60 min, 1 min = 60 sec

Time units roll over every 60

Elapsed Time

elapsed = end − start

Difference between two times

Borrowing

2:10 − 1:30 → 1:70 − 1:30 = 40 min

If minutes are short, swap 1 hour = 60 min

🎯 Key Points

①1 hour = 60 min, 1 min = 60 sec

②Short = hour, long = minute

③Elapsed = end − start

④If minutes short → borrow 60

⑤A day = 24 hours = 1440 min

Examples and Unit Test

Example 1

A movie starts at 2:20 and runs for 1 hour 40 minutes. What time does it end?

Add the run time 1 h 40 min to the start time 2:20.

20 min + 40 min = 60 min = 1 hour. 2:00 + 1 h + 1 h = 4:00. The answer is 4:00.

▸ 4:00

End time = start time + duration.

Example 2

Homework started at 3:50 and finished at 4:30. How long did it take?

Subtract start from end. The minutes are short, so borrow 1 hour as 60 minutes.

4:30 → 3:90. 90 − 50 = 40 min, 3 − 3 = 0 h. The time taken is 40 minutes.

▸ 40 minutes

If minutes are short, borrow 1 hour (= 60 minutes) from the upper place.

Unit Test

How many minutes is 2 hours 30 minutes in all?

①150 min

②230 min

③90 min

④120 min

▸ ① 150 min

2 hours = 2 × 60 = 120 minutes.

120 min + 30 min = 150 min.

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Finding Patterns