Adding and subtracting time
We can add or subtract time just like numbers, but we keep hours and minutes in separate columns. Remember that 60 minutes make 1 hour.
Key idea
Add minutes to minutes and hours to hours. If the minutes reach 60 or more, change 60 minutes into 1 hour.
Regrouping
When minutes add up to 60 or more, carry an hour. When subtracting and there are not enough minutes, borrow 1 hour = 60 minutes.
Worked example
40 minutes + 35 minutes = 75 minutes. Since 75 = 60 + 15, this becomes 1 hour 15 minutes.
Subtraction may need borrowing. To work out 3 hours − 1 hour 20 minutes, there are no minutes to take 20 from, so we borrow: 3 hours becomes 2 hours and 60 minutes. Now 60 − 20 = 40 minutes and 2 − 1 = 1 hour, giving 1 hour 40 minutes. We can check by adding back: 1 hour 40 minutes + 1 hour 20 minutes = 3 hours.
Remember
- Line up hours and minutes.
- 60 minutes = 1 hour when carrying or borrowing.
- Check your answer makes sense.