Work Efficiency — Fundamental Concepts

Fundamental Concepts

Choose a unit of work

Treat the whole job as one unit, or choose a convenient multiple of the individual completion times. If A takes 12 days and B takes 18 days, using 36 work units gives rates of 3 and 2 units per day. Together they complete 5 units daily and need 36/5, or 7.2 days, under the constant-rate assumptions.

Compare rate and time correctly

If A is 25% more efficient than B, their rates are in the ratio 5:4. Their times for the same job are therefore 4:5. A's time is 20% less than B's, not 25% less. The percentage base changes when the comparison is inverted.

Split changing arrangements

When a worker leaves, calculate work completed before the change and then use the new rate for the remainder. Do not apply the initial combined rate to the entire duration. For a pipe-and-leak analogy, incoming flow adds and outgoing flow subtracts, provided the rates are constant as stipulated.

Check the model

Real teams may face coordination limits, but an elementary exercise usually states or implies independent constant contributions. Keep those assumptions visible. A combined completion time should be shorter than either individual time when both rates are positive. If the net rate is zero or negative, the task cannot be completed by extending the same arrangement indefinitely.