Åk 6–9

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2.9 Unit Conversion
Imagine if we were to express all time in seconds.

- How long is it until summer break?
- It’s 2,419,200 seconds (2 weeks).

- How old are you?
- I am 473,364,000 seconds (15 years).

It would not be very practical.  Instead we express time in appropriate units so that the number don’t become so big or small that it would be difficult to understand.

It is important that you can convert different time units.

 1 year = 365.25 days 1 day = 24 hours 1 hour = 60 minutes 1 minute = 60 seconds

Example A

Express 12 hours in seconds.

12 hours: 12 · 60 min = 720 min
720 min: 720 · 60 s = 43,200 s

Answer: 12 hours is equal to 43,200 seconds.

Example B

Express 3,628,800 s in days.

3,628,800 s: 3,628,800 ÷ 60 = 60,480 min
60,480 min: 60,480 ÷ 60 = 1,008 h
1,008 h: 1,008 ÷ 24 = 42 days

Answer: 3,628,800 s is equal to 42 days.

Example C

How many minutes is 2.5 hours?

Here it is important to remember that 0.5 h = 30 minutes.
2.5 h: 2.5 · 60 = 150 min

Answer: 2.5 hours is equal to 150 minutes.

Example D

Expresss 23.72 days in hours, minutes and seconds.

23.72 days: 23.72 · 24 = 569.28 h
0.28 h: 0.28 · 60 = 16.8 min
0.8 min: 0.8 · 60 = 48 s

Answer: 23.72 days is equal to 569 h 16 min and 48 s.

Example E

Add 2 h 39 min 27 s with 1 h 25 min 44 s

2 h + 1 h = 3 h
39 min + 25 min = 64 min = 1 h 4 min
27 s + 44 s = 71 s = 1 min 11 s

Add each of the different time units:
3 h + 1 h = 4 h
4 min + 1 min = 5 min
11 s

Answer: 4 h 5 min 11 s