Exploring measures
Time
Time does not come in tens and hundreds — there are 60 minutes in an hour. In this section we convert between time written as a decimal (like 3.7 hours) and time written in mixed units (like 3 hours and 42 minutes).
Why time is tricky
Units of time do not go up in 10s and 100s. There are 60 minutes in an hour and 60 seconds in a minute, so you cannot just read the decimal part of a number of hours as minutes. For example, 12.5 hours is NOT 12 hours 5 minutes.
Tenths of an hour
There are 60 minutes in 1 hour, so 0.1 (one tenth) of an hour is 60 ÷ 10 = 6 minutes. So 0.7 of an hour = 7 × 6 = 42 minutes.
From decimal hours to hours and minutes
Split the number into whole hours and the decimal part. Then change the decimal part into minutes by multiplying it by 60 (or multiply the tenths by 6).
From hours and minutes back to decimal hours
Divide the minutes by 60 to get the decimal part, then add the whole hours. For example, 30 minutes ÷ 60 = 0.5, so 2 hours 30 minutes = 2.5 hours.
Dividing a time equally
Divide the number of hours by the number of shares. 5 ÷ 2 = 2.5 hours, which is 2 hours 30 minutes — not 2 hours 5 minutes. Remember to change the decimal part into minutes carefully.
Worked examples
Converting 3.7 hours to hours and minutes
- Split 3.7 into 3 whole hours and 0.7 of an hour.
- There are 60 minutes in an hour, so 0.7 × 60 = 42 (or 7 × 6 = 42).
- Put the parts back together.
Answer: 3.7 hours = 3 hours and 42 minutes.
Using tenths of an hour
- 0.1 of an hour is 6 minutes.
- 0.4 of an hour is four tenths.
- Multiply: 4 × 6.
Answer: 0.4 hours = 24 minutes.
Converting hundredths (9.25 hours)
- Split 9.25 into 9 whole hours and 0.25 of an hour.
- Change the decimal part into minutes: 0.25 × 60 = 15.
Answer: 9.25 hours = 9 hours and 15 minutes.
From hours and minutes to a decimal
- Keep the 2 whole hours.
- Change the 30 minutes into a decimal: 30 ÷ 60 = 0.5.
- Add: 2 + 0.5.
Answer: 2 hours 30 minutes = 2.5 hours.
Dividing a time equally
- Share 5 hours between 2 children: 5 ÷ 2 = 2.5 hours.
- Change 0.5 of an hour into minutes: 0.5 × 60 = 30.
Answer: Each child gets 2 hours and 30 minutes.
Where you see this in real life
- Sharing time on a games console fairly between children.
- Splitting the hours a basketball court is open between different groups.
- Recording and comparing marathon running times.
- Reading a bus or flight timetable.
Key words
- Hour
- A unit of time equal to 60 minutes.
- Minute
- A unit of time equal to 60 seconds; there are 60 minutes in an hour.
- Second
- The smallest of these units of time; there are 60 seconds in a minute.
- Interval
- A length of time between two moments.
- Convert
- To change an amount from one form to another, such as decimal hours to hours and minutes.