15Production Productivity CostsMedium1 mark
A firm has the following set of costs at different levels of output.
| output | total fixed costs $ | total variable costs $ |
|---|---|---|
| 10 | 100 | 600 |
| 20 | 100 | 900 |
| 30 | 100 | 1100 |
| 40 | 100 | 1900 |
At which level of output is the average total cost at its lowest level?