For a spur gearset with = 20, while avoiding interference, find: (a) The smallest pinion tooth

Question:

For a spur gearset with φ = 20◦, while avoiding interference, find:
(a) The smallest pinion tooth count that will run with itself
(b) The smallest pinion tooth count at a ratio mG = 2.5, and the largest gear tooth count possible with this pinion
(c) The smallest pinion that will run with a rack