An ideal two-stage workload calculation

A fictional analysis team processes records at a constant rate in an ideal planning model. Analyst A can complete a fixed job alone in 12 days and analyst B can complete the identical job alone in 18 days. Analyst A works alone for 3 days before Bisavailable; both then work together until the job is done. Assume their rates add, neither makes errors and there is no coordination overhead. A planner incorrectly averages twelve and eighteen days to estimate their joint completion time. Another planner uses the full-job joint time even after counting the first three days. Use fractions of the same fixed job throughout. These figures are exercise assumptions rather than claims about actual worker productivity or a recommendation about staffing an operational team.