T1_LO10 · lo-yr9-time
Time conversions use fixed facts: $1 h=60 min$, $1 min=60 s$, $1 day=24 h$. Elapsed time is the difference between a start and finish time.
Steps
Convert to the same unit if needed.
Use 24-hour time if it helps avoid mistakes.
For elapsed time, count up from the start to the end.
For finish time, add the duration to the start time.
Key facts
$2 h=120 min$
$3 min=180 s$
$15{:}30$ is 3:30 pm
$90 min=1 h 30 min$
Treating 2.5 hours as 2 hours 50 minutes. Since 0.5 of an hour is half of 60 minutes, 2.5 hours is 2 hours 30 minutes.
Convert $150 min$ to hours and minutes.
Convert 7:15 pm to 24-hour time.
Find the time 45 minutes after 2:30 pm.
Example 1: elapsed time
A train leaves at 8:45 am and arrives at 11:20 am.\[8{:
45\to9{:}00=15 min\]$$ 9{:}00\to11{:}00=2 h $$$$ 11{:}00\to11{:}20=20 min $$Total: $2 h 35 min$.}
Example 2: finish time
A movie starts at 14:30 and lasts 1 h 55 min.\[14{:
30+1 h=15{:}30\]$$ 15{:}30+55 min=16{:}25 $$Finish time: 16:25.}
Example 3: speed
A car travels 240 km in 3 h.\[speed=\frac{240
{3}=80 km/h\]}
Example 4: decimal hours
Convert 1.6 h to minutes.$$ 1.6\times60=96 min $$