Time and timetables (Edexcel GCSE Maths): Revision Notes
Time and timetables
Understanding time formats
There are two main ways to write time: the 12-hour clock and the 24-hour clock.
12-hour clock uses numbers from 1 to 12 with am (morning) or pm (afternoon/evening):
- 8.15 am means 8:15 in the morning
- 4.50 pm means 4:50 in the afternoon
- 12.00 midday means noon
- 12.00 midnight means the start of a new day
24-hour clock uses numbers from 00:00 to 23:59 without am or pm:
- 08:15 means 8:15 in the morning
- 16:50 means 4:50 in the afternoon
- 12:00 means midday
- 00:00 means midnight
The 24-hour clock is commonly used in timetables because it removes confusion about whether a time is morning or evening. This makes it much clearer for transport schedules and official timing.
Converting hours and minutes
Remember that there are 60 minutes in one hour. This is essential for all time calculations and forms the foundation for working with time conversions.
Worked Example: Converting Fractional Hours
When converting fractional hours to minutes:
- hour = 30 minutes
- hour = 45 minutes
- hours = 2 hours + 15 minutes = 135 minutes
You can write times in different ways. For example, 2 hours and 15 minutes can be written as "2 hours and 15 minutes" or "135 minutes total". Both representations are mathematically equivalent.
Reading timetables
Timetables show departure and arrival times for transport services. They usually use the 24-hour clock format to avoid confusion.
Method for Reading Timetables:
When reading a timetable, follow these steps systematically:
- Find your starting location in the first column
- Read across to find departure times
- Find your destination and read down to find arrival times
- Check which column shows the service you want to catch
For example, if a bus leaves Crook at 10:45 and arrives in Hexham at 11:15, the journey time is 30 minutes.
Calculating journey times
To work out total journey time, add each section step by step. This methodical approach prevents calculation errors and ensures accuracy.
Method for Calculating Journey Times:
- Write down your starting time
- Add each time interval one at a time
- Convert minutes to hours when you reach 60 minutes or more
- Write down your final arrival time
Worked Example: Step-by-Step Journey Calculation
Calculate the total journey time:
- Start: 11.30 am
- Add 15 minutes → 11.45 am
- Add 25 minutes → 12.10 pm
- Add hours (90 minutes) → 1.40 pm
- Final arrival time: 1.40 pm
Total journey time: 2 hours and 10 minutes
Always work through time calculations methodically to avoid errors and double-check your working.
Time zones
Different places around the world have different times. When it's afternoon in one city, it might be morning in another city.
Time differences occur because:
- The Earth rotates, so different places experience day and night at different times
- Countries set their clocks to match their local daylight hours
- Some places are several hours ahead or behind others
When solving time zone problems, first determine whether one location is ahead of or behind the other, then add or subtract the time difference accordingly. Always be clear about which direction you're converting.
Summary
Key Points to Remember:
- 60 minutes = 1 hour - this is fundamental for all time calculations
- 24-hour clock removes am/pm confusion and is used in most timetables
- Add time intervals step by step rather than trying to do it all at once
- Timetables show both departure and arrival times - read carefully to find the right information
- Time zones mean different places have different times simultaneously