Gear A has 72 teeth and gear B has 48 teeth. How many complete revolutions does gear A make when gear B makes 9 complete revolutions?

I’m assuming that these gears are connected, so that their teeth interlock and when one turns the other one does, too?

When gear B moves 5 teeth, gear A moves 5 teeth.

When gear B makes 9 complete revolutions, that means its 48 teeth all touch gear A 48 × 9 = 432 times.

Gear B’s teeth must also touch gear A 432 times, so we can calculate the revolutions it makes by dividing: 432/72 = 6.