SME
Grade 3 Math · Problem type
Elapsed time and end time
Use this for “It starts at 3:45 and takes 35 minutes. When does it end?” and “How long?”
Diagram
Start 3:45, end 4:20: 35 minutes.
This is an example. Type your own values to start a new problem.
Start hour
:
Start minutes
+
Minutes it takes
minutes
=
End hour
:
End minutes
Formulas
45 minutes + 35 minutes ends at 20 minutes past the hour
Start minutes + minutes it takes = end minutes, past the hour
3:45 + 35 minutes = 4:20
Start hour:start minutes + minutes it takes = end hour:end minutes
Assumptions
•
Count on from the start: to the next hour, then whole hours, then the minutes left.
•
After 12:59 the clock starts again at 1:00.
•
60 minutes make 1 hour: change hours to minutes first. Times up to 600 minutes (10 hours).
Step-by-step
WE KNOW
Start hour: 3
Start minutes: 45
Minutes it takes: 35
FIND
end minutes, end hour
Step 1 · Find end minutes
45 minutes + 35 minutes ends at ? minutes past the hour
Start minutes + minutes it takes = end minutes, past the hour
Count on from the start time: to the next hour, then whole hours, then the rest.
3:45 → 4:00 is 15 minutes
4:00 → 4:20 is 20 minutes
15 + 20 = 35 minutes
End minutes = 20
Step 2 · Find end hour
3:45 + 35 minutes = ?:20
Start hour:start minutes + minutes it takes = end hour:end minutes
The last jump lands at the end time: read its hour.
End hour = the hour 35 minutes after 3:45
End hour = 4 (4:20)
Check
Put the numbers back in. Both sides should match.
45 minutes + 35 minutes ends at 20 minutes past the hour ✓
3:45 + 35 minutes = 4:20 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.