If the price is X, the sales volume will be reduced by 10*(x-50), so the sales volume is 500- 10*(x-50).

So profit is the profit of each commodity * sales volume: [500- 10*(x-50)]*(x-40),

Simplify to (500- 10x+500)*(x-40), continue to (1000- 10x)*(x-40), and finally get.

10( 100-x)(x-40), that is to say, find the maximum x value of this formula.

-10[(x-70) squared -900], so x=70 and the profit is 9000.

answer