Mathematics (Core)Exam code: 0580
Time, Currency and Conversions
Number
Finding a duration
- Subtracting clock times directly can give a wrong answer, because an hour is 60 minutes, not 100
- Count on instead: go up to the next whole hour, then in whole hours, then the remaining minutes
- From 14 25 to 18 10: 35 minutes reaches 15 00, then 3 hours reaches 18 00, then 10 minutes more, giving 3 hours 45 minutes
- Adding a duration works the same way, carrying 60 minutes as one hour
Exam tip
Write the length of time first
Working out a clock time from another time and a length of time was set in 8 of the 22 papers. When that length must be found first, by adding several times, changing minutes to hours or dividing a distance by a speed, the schemes give it a mark even if the clock time slips. Write it on its own line in hours and minutes, such as 200 minutes = 3 h 20 min, before adding it on.
Worked example
Adding a duration to a time
A bus leaves at 14 35 and the journey takes 2 hours 50 minutes. Work out the arrival time.
Solution:
- Add the hours first: 14 35 + 2 hours = 16 35
- Then add the minutes: 35 + 50 = 85 minutes
- 85 minutes is more than an hour, so exchange 60 of them for 1 hour, leaving 25
- 16 35 + 50 minutes = 17 25
- The bus arrives at 17 25
- Adding 2.50 to 14.35 on a calculator gives 16.85, which is not a time at all: minutes are sixtieths, not decimals
Worked example
An arrival time after midnight
A coach leaves at 19 45 and the journey takes 7 hours 25 minutes. Find the arrival time.
Solution:
- Add the hours first: 19 45 + 7 hours = 26 45
- Add the minutes: 45 + 25 = 70 minutes, which is 1 hour 10 minutes, so the time reaches 27 10
- A day has only 24 hours, so take 24 off the hours: 27 10 is 03 10 the next day
- The coach arrives at 03 10, which is 3.10 am