IMPT: Please take note - Addition and Subtraction of Time

Dear pupils,

Sorry if I've caused some confusion. Do take note of the following points regarding addition and subtraction of time:

We can only add or subtract the duration of time:

E.g. 2h 30 min + 3h 40 min = 5h 70min = 6h 10min (correct!)

However, we cannot add or subtract the duration of time with time:

E.g. 2.30pm + 1h 30min = 4pm (wrong!)

Please note that the above working is unacceptable. Marks will be deducted if you write it this way.  Instead you can only show your working(s) using a time line.

                     +1h                   +30min
E.g. 2.30pm --------->3.30pm-------->4.00pm

I will explain in details on Monday next week.