We work with time in almost every area of our life, so knowing how to add and subtract time, calculate the time between events, or even use a $24$24 hour clock are important. Let's look at some common ways we may need to work with time.
When we want to find the difference between times we can construct a subtraction expression in a similar way to how we usually subtract two numbers - but it's important to remember that there are $60$60 minutes in an hour, so we have to adjust our counting accordingly. People often forgot this in the calculations which can lead to errors. For example, the difference between $6$6 pm and $5:30$5:30 pm is $30$30 minutes. This is not the same as $6-5.3$6−5.3 which people commonly (and mistakenly) write, as this results in $0.7$0.7 (which they then interpret as $70$70 minutes - again, mistakenly).
Similarly, when adding time, once the total number of minutes reaches $60$60 minutes we add $1$1 to the hours instead.
Add $2$2 hours and $45$45 minutes to $5:25$5:25 pm.
Do: We could start by first adding the minutes $25+45$25+45 which is equal to $70$70 minutes. We can think of this as $60$60 minutes $+10$+10 minutes, which is $1$1 hour and $10$10 minutes. Now add the hours $5+2+1$5+2+1 and we get $8$8. So adding $2$2 hours and $45$45 minutes onto $5:25$5:25 pm takes us to $8:10$8:10 pm.
Reflect: Alternatively, we could view the problem more visually. Starting at $5:25$5:25 there are $35$35 minutes until $6:00$6:00. This leaves us with $2$2 hours and $10$10 minutes to add. First add the $10$10 minutes to reach $6:10$6:10 and then $2$2 hours to reach our final answer of $8:10$8:10 pm.
$60$60 minutes makes $1$1 hour
Find the value of
$3$3 hours $3$3 minutes $+$+ $3$3 hours $29$29 minutes
$\editable{}$ hours $\editable{}$ minutes
James went to a movie at $11:50$11:50 am. The movie went for $1$1 hour and $10$10 minutes.
Would the movie finish in the am or pm?
am
pm
Complete the statement:
The movie finishes at $\editable{}$$:$:$\editable{}$$\editable{}$ pm.
Evaluate $6$6 hours $10$10 minutes $-$− $2$2 hours $30$30 minutes.
$\editable{}$ hour(s) $\editable{}$ minute(s)
If a bus departs at $9:20$9:20 am and arrives at its final destination at $12:55$12:55 pm calculate the the length of the journey.
Think: We can do this by breaking the time down into smaller parts. This can be done visually as follows:
Do: Add the minutes together, remembering that once the minutes reach $60$60, we can add another hour.
From $9:20$9:20 am until $10:00$10:00 am | $=$= | $40$40 min | |
From $10:00$10:00 am to $12:00$12:00 pm | $=$= | $2$2 h | |
From $12:00$12:00 pm to $12:55$12:55 pm | $=$= | $55$55 min | |
Total: | $=$= | $2$2 h | $95$95 min |
$95$95 minutes is $60$60 minutes + $35$35 minutes. ($1$1 hour and $35$35 minutes)
Thus, the journey was $3$3 hours and $35$35 minutes in duration.
A song clip starts playing at $7$7:$55$55 pm and finished at $8$8:$11$11 pm. How long is the song clip in minutes?
A taxi departs at 13:32 from Sydney and arrives at 20:14 at Melbourne. How long did the taxi take for the trip?
The trip took $\editable{}$ hour(s) and $\editable{}$ minute(s)
We can also use our calculators to help with some of these calculations.
Calculate $3$3 hours $40$40 minutes - $1$1 hour $55$55 minutes.
Think: We can put it in the calculator using the DMS button like we would if we were to calculate angles.
Do:
Hence, the answer is $1$1 hour $45$45 minutes.
Reflect: Try the practice questions above again, this time using the calculator in this way. Do you get the same answers as before?