Time between two times

In your book, Maths Mela (Chapter 12), Raghav practises yoga in the morning, and we ask how much time he spent: the time that passed between when he started and when he finished. This is called the time elapsed.

When both times are in the same hour, just take away the minutes. From 01:15 p.m. to 01:42 p.m., the hour stays at 1 and the minutes go from 15 to 42. 42 − 15 = 27, so 27 minutes passed. When only the hour changes, count the hours. From 03:18 p.m. to 08:18 p.m., the minutes stay at 18 and the hours go from 3 to 8: that is 5 hours.

When both change, count the whole hours first, then the extra minutes. From 09:15 a.m. to 11:30 a.m.: from 09:15 a.m. to 11:15 a.m. is 2 hours, and from 11:15 a.m. to 11:30 a.m. is 15 more minutes. So the time elapsed is 2 hours 15 minutes.

The book does the same with the 24-hour clock. Raghu leaves his house at 08:00 hours and reaches his Nana ji's house at 09:05 hours. From 08:00 hours to 09:00 hours is 1 hour, and then 5 more minutes. So Raghu took 1 hour 5 minutes.