A motor drives a rotating display platform through a compound gear system.
| Gear | Number of teeth | Connection |
|---|---|---|
| A | 20 | connected to the motor and meshes with B |
| B | 40 | fixed to C on the same shaft |
| C | 14 | meshes with D |
| D | 42 | connected to the display platform |
Gears B and C rotate at the same rate and in the same direction.
Gear D must turn anticlockwise at 30 revolutions per minute. The motor has four settings.
| Setting | Rate of gear A in revolutions per minute | Direction of gear A |
|---|---|---|
| 1 | 5 | anticlockwise |
| 2 | 60 | clockwise |
| 3 | 90 | clockwise |
| 4 | 180 | anticlockwise |
How should gear A turn?
Setting 1: 555 revolutions per minute anticlockwise.
Setting 4: 180180180 revolutions per minute anticlockwise.
Setting 3: 909090 revolutions per minute clockwise.
Setting 2: 606060 revolutions per minute clockwise.