Doing the math

I have to do this every time I do a time lapse. Assume normal is 30 frames per second.

Seconds per frame	X Normal	Math	Hour passes in
1 frame every 1 second	30	60 min / 30 = 2/1 of a min	2 min
1 frame every 3 seconds	90	60 min / 90 = 2/3 of a min	45 sec
1 frame every 5 seconds	150	60 min / 150 = 2/5 of a min	24 sec