If you find the least common multiple of both numbers, this will give you the information you will need to get your answer. Each revolution would include all teeth going around. The list of multiples for 24 are 24, 48, 72, 96, 120. The list for 40 are 40, 80, 120. This means at 120, they would be in the same place again. For the first gear to get to 120, it would take 5 rotations the fifth number in the list of multiples for 24). I hope this helps!
