39
Hours, minutes and seconds
Textbook: Part 1, lesson 39, pp. 120–122
GoalKnow how hours, minutes and seconds are related; calculate with units of time.
New words
hour · soatminute · minutsecond · sekundday (24 hours) · sutka
Explanation
1 hour = 60 minutes, 1 minute = 60 seconds, so 1 hour = 3 600 seconds. 1 day = 24 hours = 1 440 minutes = 86 400 seconds. When adding or subtracting time, put like units under each other; if a unit reaches 60 it moves up, and if there is not enough you borrow 1 from the larger unit.
Worked examples
37 min = 37 × 60 = 2 220 s; 6 h = 6 × 60 = 360 min.
1 day = 24 × 60 × 60 = 86 400 s. 90 000 s > 86 400 s, so 90 000 s is 3 600 s (1 hour) longer than a day.
Class activity
“Count the time”: with a stopwatch, children count 10, 20 and 30 seconds. Then they guess how many claps fit into a minute and test it.
Practice
1
How many minutes are in 15 hours?
900
2
How many seconds are in 37 minutes?
2220
3
How many seconds are in 1 day?
86400
4
5 h 13 min − 2 h 46 min = ?
2 h 27 min
5
7 min 25 s + 3 min 45 s = ?
11 min 10 s
6
A craftsman is paid 250 so‘m per minute of work. How much does he earn in 8 hours?
120000