As the firm requires a 20% profit on each increment of investment, we should examine the B- A increment of $200,000. (With only a 16% profit rate, C is unacceptable.)
Alt. Initial Cost Annual Profit Change in Cost Change in Profit Change in Profit Rate
A $100,000 $30,000
B $300,000 $66,000 $200,000 $36,000 18%
C $500,000 $80,000
With the alternative A it produces a 30% profit rate. The $200,000 increment of investment of B rather than A, that is, B- A, yield an 18% profit rate and is not acceptable. Thus it means Alternative B with an overall 22% profit rate can be considered as made up of Alternative A plus the B- A increment. Because the B-A increment is not acceptable, Alternative B should not be adopted.
Therefore the best investment of $300,000, for instance, would be Alternative A (annual profit = $30,000) plus $200,000 elsewhere (which is yielding 20% or $40,000 annually). At this combination firm yields a $70,000 profit, which is better than Alternative B profit of $66,000.