At a price of $1.00, a dealer can sell 1000 articles that cost him 60 cents each. For each cent that the lowers the price, he can increase the number sold by 50. What price will maximize the profit?
Source: Rosenberg, R.L. (1984). Elementary Calculus: Course Notes. Ottawa, Canada: Holt, Rinehart and Winston. (Exercise 2: Question 14, p. 11)