Formula and example
How it is calculated
Combined rate=1/tA+1/tB. Continuous joint duration=1/(1/tA+1/tB). After B leaves, A completes the remainder.
Worked example
A needs six hours alone and B needs three. Together they take two hours. If B leaves after one hour, the total duration becomes four hours.
Things to check
- The task must be divisible and the two work rates must add without coordination losses.
- Setup times, dependencies between steps and declining performance are not modelled.
Frequently asked questions
Why not simply average the times?
The fractions completed per hour are added. Someone who finishes in three hours completes one third each hour; someone who takes six hours completes one sixth.