Very good Crazy Voyager, that's how I work them out too
It's also handy to memorise time units as a fraction of an hour:
E.g. 10mins = 1/6 hours
4mins = 1/15 hours
It saves trying to work them out for the first time on the day and helps on the questions such as...
'A plane is travelling at 196kts, how far does it travel in 2hr 8mins.'