Adding and subtracting time
When we add or subtract time, we work with hours and minutes separately. The tricky part is that 60 minutes = 1 hour, not 100. So when minutes reach 60 or more, we change them into hours.
Worked example
Add 2 h 45 min + 1 h 30 min.
Minutes: 45 + 30 = 75 min = 1 h 15 min.
Hours: 2 + 1 = 3 h, plus the extra 1 h = 4 h.
Answer = 4 h 15 min.
Subtracting with borrowing
If we do not have enough minutes, we borrow 1 hour (= 60 minutes). For 5 h 10 min − 2 h 30 min: change 5 h 10 min to 4 h 70 min, then 70 − 30 = 40 min and 4 − 2 = 2 h, giving 2 h 40 min.
Remember
- Add or subtract hours and minutes separately.
- If minutes reach 60, change 60 min into 1 hour.
- When subtracting, borrow 1 hour = 60 minutes if needed.