Elapsed Time and Timetables

What you will learn

• Find how long there is between two times.
• Find an end time from a start time and a duration.
• Read a simple timetable.

Before you start: you should be able to tell the time in 12-hour and 24-hour form. See 12-Hour and 24-Hour Time.

The idea

Elapsed time is the time that passes between a start and an end. A good way to find it is to jump to the next whole hour, then jump by whole hours, then add any minutes left over.

Finding an end time

Add the duration in steps. For $14{:}25$ plus $50$ minutes: add $35$ minutes to get to $15{:}00$, and then the remaining $15$ minutes, to reach $15{:}15$.

Reading a timetable

A timetable lists the time each service reaches each stop. To find a journey time, take the time at the start stop away from the time at the end stop.

Hours and minutes

Remember there are $60$ minutes in an hour, so you cannot subtract like ordinary numbers. $10{:}10 - 9{:}50$ is $20$ minutes, not $60$.

Worked examples

Example 1: How long?

How long is it from $09{:}50$ to $11{:}10$?

1. $09{:}50$ to $10{:}00$ is $10$ minutes.
2. $10{:}00$ to $11{:}00$ is $1$ hour.
3. $11{:}00$ to $11{:}10$ is $10$ minutes.
4. Total: $1$ hour $20$ minutes.

Answer: $80$ minutes

Example 2: End time

A film starts at $18{:}20$ and lasts $1$ hour $35$ minutes. When does it end?

1. $18{:}20 + 1$ hour $= 19{:}20$.
2. $19{:}20 + 35$ minutes $= 19{:}55$.

Answer: $19{:}55$ (five to eight in the evening)

Example 3: Timetable

Using the timetable, how long is the journey from Bridge to Harbour?

1. Bridge $08{:}40$ to $09{:}00$ is $20$ minutes.
2. $09{:}00$ to $09{:}35$ is $35$ minutes.
3. $20 + 35 = 55$.

Answer: $55$ minutes

Tip: draw a quick number line. Jumping to the next hour keeps the sums small.

Why it matters

Planning a journey, timing a recipe, working out when a film finishes and checking how long you have left all use elapsed time. It is a skill you use daily without noticing.