What efficiency would you be working on in this problem?

Question

So let's say a specific task would take 80 seconds by yourself. But you have 3 other friends working on the task with you. The task now only takes 28.57 seconds. So if when you were working by yourself you were working at 100% efficiency, How much slower are you and your friends while working together?

Answer 1

From here:

The efficiency ratio measures whether the production output for a period in a production cost centre took more or less direct labour time than expected. It is calculated as: $$\dfrac{\text{Expected direct labour hours of actual output}}{\text{Actual direct labour hours worked}} * 100\%$$

So, in your case,

$$\text{Efficiency ratio} = \dfrac{20}{28.57} * 100\% \simeq 70.004\%$$