Learning Curve

During the following year, a 90% learning curve was observed in making a product. The cumulative production at the end of the third quarter was 50 units. After producing 50 units, the learning effect ended, and all subsequent units took the same time to make.

Required: What is the standard cost per unit for the fourth quarter assuming the learning curve had reached a steady state ie peak efficiency was reached after the 50th unit was produced?

In the answer, it compared 51 units with 50 units. Why it is not by comparing 50 units with 49 units, if the learning curve stopped at 50? By applying the Y-axb for 51 units, aren’t you applying the learning curve also in the 51st unit, thus the learning curve is stopped in 51 instead of 50 units as told?

Thank you in advance John.

regards,

Marylise