Now add the minutes. 15 minutes + 45 minutes = 60 minutes.
60 minutes is a whole hour, so it is not written as 07:60. Exchange it: 60 minutes = 1 hour, 0 minutes.
Carry that hour: 07 + 1 = 08, and the minutes become 00.
So she reached home at 08:00 PM.
06 hr : 15 min + 01 hr : 45 min ───────────── 07 hr : 60 min 60 min = 1 hour, so carry 1 = 08:00 PM
Why we cannot write 07:60: A clock never shows 60 minutes. As soon as the minutes reach 60, they turn into one more hour and the minute count starts again at 0. This is the base-sixty carry, and it is the only thing that makes time sums different from ordinary addition.
Check it yourself: Go backwards from 08:00 PM. Take away 1 hour → 07:00 PM. Take away 45 minutes → 06:15 PM ✓ That is where she started.
Q5.
Ragini took 1 hour 10 minutes to do her homework. She finished it at 09:40 PM. What time did she start?
Answer
Ragini started at 08:30 PM.
This time we know the end, so we must walk backwards.
Go back the whole hour first. 09:40 PM − 1 hour = 08:40 PM.
Now go back the minutes. 40 minutes − 10 minutes = 30 minutes.
So the starting time was 08:30 PM.
09 hr : 40 min (finished) − 01 hr : 10 min (time taken) ───────────── 08 hr : 30 min → 08:30 PM
No borrowing was needed here because 40 minutes is bigger than 10 minutes. If she had finished at 09:05 PM instead, we could not take 10 from 5. Then we would borrow 1 hour and turn it into 60 minutes: 5 becomes 65, and 65 − 10 = 55, giving 08:55 PM.
Check it yourself: 08:30 PM + 1 hour = 09:30 PM, and + 10 minutes = 09:40 PM ✓
Q6.
A group of children left for a picnic at 08:30 AM. They returned after 4 hours and 10 minutes. At what time did they return?
Answer
They returned at 12:40 PM.
Add the hours. 08:30 AM + 4 hours: 8 → 9 → 10 → 11 → 12. So we reach 12:30.
Watch out for noon. Once we pass 12 o'clock in the middle of the day, the label changes from AM to PM. 12:30 in the middle of the day is 12:30 PM.
Add the minutes. 30 + 10 = 40 minutes. This is less than 60, so nothing is carried.
Why the AM turned into PM: AM covers midnight to noon, PM covers noon to midnight. The picnic started in the morning and finished after 12 noon, so it crossed the changeover point.
In 24-hour format this is much simpler: 08:30 hours + 4:10 = 12:40 hours, with no AM or PM to worry about at all. That is exactly why timetables use it.
Q7.
Raji started her homework at 06:00 PM. She finished her homework in 1 hour 30 minutes. At what time did she finish?
Since 0 + 30 = 30, which is less than 60, there is nothing to carry.
06 hr : 00 min + 01 hr : 30 min ───────────── 07 hr : 30 min → 07:30 PM
On the clock face: the hour hand slides from 6 to halfway between 7 and 8, and the minute hand goes once round and then half way, stopping at the 6. Half past seven.
Q8.
Alya goes out to play at 05:30 PM and comes back after 1 hour 10 minutes. At what time does she come back?
Answer
Alya comes back at 06:40 PM.
Add the hour. 05:30 PM + 1 hour = 06:30 PM.
Add the minutes. 30 + 10 = 40 minutes.
40 is less than 60, so the hour does not change again. She is back at 06:40 PM.
05 hr : 30 min + 01 hr : 10 min ───────────── 06 hr : 40 min → 06:40 PM
Check it yourself: 1 hour 10 minutes = 70 minutes. From 05:30 PM, 30 minutes takes her to 06:00 PM, and the remaining 40 minutes takes her to 06:40 PM ✓
Q9.
If the lunch break of a school starts at 12:30 PM and ends in 35 minutes, what time will lunch end?
Answer
Lunch will end at 01:05 PM.
Add the minutes. 30 + 35 = 65 minutes.
65 is more than 60, so we must exchange. 65 = 60 + 5.
The 60 becomes one whole hour and is carried to the hour column. Only 5 minutes stay behind.
12 hr : 30 min + 00 hr : 35 min ───────────── 12 hr : 65 min 65 min = 60 min + 5 min = 1 hr 5 min 12 hr + 1 hr = 13 hr → 01:05 PM
Why 12 turns into 1 and not 13: On the 12-hour clock the numbers go up to 12 and then start again at 1. So the hour after 12 noon is 1 PM. In the 24-hour format, though, we really do write 13:05 hours.
Check it yourself: From 12:30 PM, 30 minutes takes you to 01:00 PM. Then 5 more minutes makes 01:05 PM. And 30 + 5 = 35 minutes ✓
Q10.
It is 08:35 PM right now. What time will it be after 8 hours and 25 minutes?
Answer
It will be 05:00 AM the next morning.
Add the hours first. 08:35 PM + 8 hours. Count on: 9, 10, 11, 12 (that is 4 hours and we are at midnight), then 1, 2, 3, 4 (four more hours). We reach 04:35 AM.
Notice the date has changed. We crossed 12 midnight, so PM became AM and it is now the next morning.
Now add the minutes. 35 + 25 = 60 minutes.
60 minutes is one whole hour, so exchange it: the minutes become 00 and one more hour is carried.
Add that hour: 04 + 1 = 05. So the time is 05:00 AM.
08:35 PM + 8 hours = 04:35 AM (next day) 35 min + 25 min = 60 min = 1 hour 04:35 AM + 25 min = 05:00 AM
Why midnight matters: Midnight is where one day ends and the next begins. Adding 8 hours to 8:35 in the night carries us right past it, so the answer is a time on the following day — early morning, when the sun is not yet up.
Easier in 24-hour format: 08:35 PM is 20:35 hours. 20:35 + 8:25 = 28:60 hours. Now tidy it up: 60 minutes = 1 hour, so 29:00 hours. And 29 − 24 = 5, so it is 05:00 hours the next day ✓ Same answer.