9. A simple mechanical device has four gears A, B, C and D such that they mesh in the order A-B-C-D. The number of teeth in these gear is 10, 21, 12, 17 respectively. If we start the mechanism from rest, how many revolutions will the largest gear have to turn before one full cycle is completed and the gears are in the position from where they started?

1. 270    

2. 340    

3. 7140

4. 285

Correct Answer :

340