The weekly cost C, in dollars, of manufacturing x lightbulbs is C(x)=7500+√125x
Solution (a) The weekly cost of manufacturing 100 lightbulbs is C(100)=7500+√125⋅100=7500+√12,500≈$7611.80
The weekly cost of manufacturing 101 lightbulbs is C(101)=7500+√125⋅101=7500+√12,625≈$7612.36
The average rate of change of the weekly cost C from 100 to 101 is ΔCΔx=C(101)−C(100)101−100≈7612.36−7611.801=$0.56
(b) The weekly cost of manufacturing 1000 lightbulbs is C(1000)=7500+√125⋅1000=7500+√125,000≈$7853.55
The weekly cost of manufacturing 1001 lightbulbs is C(1001)=7500+√125⋅1001=7500+√125,125≈$7853.73
The average rate of change of the weekly cost C from 1000 to 1001 is ΔCΔx=C(1001)−C(1000)1001−1000≈7853.73−7853.551=$0.18
(c) Part (a) tells us that the cost of manufacturing the 101st lightbulb is $0.56. From (b) we learn that the cost of manufacturing the 1001st lightbulb is only $0.18. The unit cost per lightbulb decreases as the number of lightbulbs manufactured per week increases.