The first unit took fifteen days to finish and the second unit was finished a mere 13.5 days later. How many more days will pass before the tenth unit is finished?
A) 91.5
B) 119.9
C) 109.3
D) 129.5

Question

Quizplus · Accepted Answer

The time taken to produce each unit decreases by a constant factor (learning curve). The second unit took 13.5 days, which is 90% of the first unit's time (15 days). Using this 90% learning curve, the time for the 10th unit can be calculated using the formula for the sum of a geometric series. The total time for 10 units is approximately 106.5 days, so 106.5 - 28.5 (time for first two units) = 91.5 days.

The First Unit Took Fifteen Days to Finish and the Second