Calculations involving time require careful use of units and notation. Time does not use base ten, so accuracy depends on remembering how units relate and converting correctly.

 

 

Understanding Time Units

Time is measured using fixed units.

 

There are:
• 60 seconds in a minute
• 60 minutes in an hour
• 24 hours in a day

 

Because these units are not based on tens, you must be careful when adding, subtracting or converting time.

 

 

Calculating Time Intervals

To find the duration between two times, count forward from the start time to the end time.

 

This can be done by:
• counting hours first
• then counting minutes
• then counting seconds if required

 

Breaking the calculation into steps helps avoid mistakes.

 

When times cross midday or midnight, take extra care to account for the change of day.

 

 

Using the 24-Hour Clock in Calculations

The 24-hour clock is often easier to use for calculations because it avoids confusion between am and pm.

 

Times are written using four digits, such as 09:40 or 17:15.

 

To calculate a time interval:
• subtract the earlier time from the later time
• convert minutes if the result is negative

 

For example, when subtracting minutes, you may need to borrow 1 hour, which is equal to 60 minutes.

 

 

Adding and Subtracting Time

When adding or subtracting time:
• add or subtract minutes first
• if minutes reach 60 or more, convert to hours
• if minutes go below zero, borrow 60 minutes from the hours

 

The same method applies when working with seconds.

 

Always check that minutes and seconds stay between 0 and 59

 

 

Solving Word Problems Involving Time

Time calculations often appear in real life contexts.

 

Examples include:
• journey times
• timetables
• start and finish times
• schedules

 

In these problems:
• identify the information given
• decide whether you are finding a duration or a finishing time
• show each step clearly

 

Writing times clearly helps prevent errors.

 

 

Common Errors to Avoid

Common mistakes include:
• treating time as base ten
• forgetting to convert between units
• mixing 12-hour and 24-hour notation
• not accounting for crossing midnight

 

Careful checking helps avoid these errors.

 

 

Key Points to Remember

Time uses units of 60 and 24, not base ten.
Durations are found by counting or subtracting times.
The 24-hour clock is useful for calculations.
Minutes and seconds must stay between 0 and 59.
Clear working improves accuracy.

 

Being confident with time calculations allows you to solve practical problems involving schedules, journeys and durations accurately.