The first candle was sold at 10$ and the store sold 2500 of them. Then they decreased to 9.50$ and sold 2800, they decreased more to 9$ and sold 3100. Find a quadratic formula that will model the profit from this based on price change. What selling price would maximize the profit? How much would that profit be?

3 answers

Suppose there are x price decreases of 50 cents. then we have profit (revenue-cost)

p(x) = (10-0.5x)(2500+300x) - (2500+300x)*c

you haven't specified how much it cost for each candle.
At first it costs 10$ per candle, then the price decreases to 9.50$ per candle then it decreases once more to 9$ per candle
those are the selling prices. But profit depends on the seller's cost, which is unknown.