Time duration problems

A train leaves at 8:15 A.M. and reaches its destination at 11:45 A.M. How long was the journey? To answer, we calculate the duration , the time between two clock readings.

What is this?

The duration between two times is the difference. Subtract the smaller time from the bigger time.

For times in the same A.M./P.M. block, this is direct.

For 8:15 A.M. to 11:45 A.M.:

• Hours: 11 − 8 = 3.
• Minutes: 45 − 15 = 30.
• Duration: 3 hours 30 minutes.

When the minutes part of the end time is smaller than the start time minutes, borrow 1 hour = 60 minutes.

For 9:50 A.M. to 11:30 A.M.:

• Minutes: 30 < 50. Borrow 1 hour. 60 + 30 = 90. 90 − 50 = 40.
• Hours: 11 − 1 = 10. 10 − 9 = 1.
• Duration: 1 h 40 min.

When start is A.M. and end is P.M., convert both to 24-hour format first, then subtract.

For 10:30 A.M. to 3:15 P.M.:

• 10:30 → 10:30.
• 3:15 P.M. → 15:15.
• Duration: 15:15 − 10:30 = 4 h 45 min.

This is also how we calculate journey times in railway timetables. Convert both stations' times to 24-hour and subtract.

Worked examples

Example 1. A film starts at 6:15 P.M. and ends at 8:45 P.M. Duration?

• Hours: 8 − 6 = 2.
• Minutes: 45 − 15 = 30.
• 2 h 30 min.

Example 2. A class starts at 10:50 A.M. and ends at 12:20 P.M. Duration?

• Convert: 10:50 and 12:20.
• 12:20 − 10:50: minutes 20 < 50, borrow 1 h → 80 − 50 = 30. Hours: 12 − 1 − 10 = 1.
• 1 h 30 min.

Example 3. A train leaves Delhi at 22:15 and reaches Bhopal at 06:45 next morning. Journey time?

• 06:45 next day = 24:00 + 06:45 = 30:45.
• 30:45 − 22:15 = 8 h 30 min.

Try it

1. From 7:20 A.M. to 9:50 A.M. , how long?
2. From 4:35 P.M. to 7:15 P.M. , how long?
3. A train leaves at 13:25 and reaches at 17:40. Duration?
4. A film of 2 h 15 min starts at 6:30 P.M. When will it end?
5. Asha started her homework at 4:20 P.M. and finished at 6:05 P.M. How long did she take?

Hands-on

School-day timer. Note when you start a chapter of homework and when you finish. Calculate the duration. Try this for 3 different tasks in a day.

Cooking timer. Help in the kitchen. Note the start time of cooking (say a dal). Note when it is ready. Calculate the duration in hours and minutes.