In real life, it is very useful to be able to work out how long it takes for something to happen, or the actual time when something will take place.
Remember that there are 60 minutes in an hour.
Adding or subtracting minutes
Adding or subtracting minutes to or from a time can be simple.
15 minutes before 7:30 p.m. is simply 7:15 p.m.
15 minutes after 7:30 p.m. is simply 7:45 p.m.
Be careful when you have to cross a whole hour.
Go to the whole hour first and then go on.
15 minutes before 7:10 p.m. is 6:55 p.m.
(Go back 10 minutes to 7 o'clock and then 5 minutes further back.)
15 minutes after 7:50 p.m. is 8:05 p.m.
(Go forwards 10 minutes to 8 o'clock and then 5 minutes more.)