Here is a non-trig way of how I look at it.
The large wheel circumference is 500 * Pi or 1570.796 mm, divided by 360 gives 4.363 mm per degree.
The small wheel circumference is 30 * Pi or 94.248 mm, divided by 20 gives 4.712 mm per pulse.
The small wheel turns 4.712 mm per pulse, so does the large wheel turn 4.712 mm.
(4.712 - 4.363) / 4.363 = 0.08.
So with every pulse the large wheel moves about 1.08 degrees at its circumference.
I imagine there are plenty of people on here that use trig every day and can probably roll out a precise formula. The trig I learned too many years ago has never been used, so I fell back on this clunky method. I hope I'm not too far off...