Question

A manufacturer can sell x items at a price of ₹ (280 - x) each .The cost of producing items is ₹ (x² + 40x + 35) Find the number of items to be sold so that the manufacturer can make maximum profit.

Answer 1

 Selling price = x . (280 - x) =  280x - x² 

Cost price = x² + 40x + 35 

Let P be the profit. 

∴ P = selling price - cost price 

= 280 x -x² - (x² + 40x + 35) 

= -2x²+ 240x - 35

`therefore "dP"/"dx" = -4"x" + 240`     ...(I)

`"dP"/"dx" = 0 => -4"x" + 240 = 0`

`therefore "x" = 60`

Differentiating (I). w.r.t. x, again 

`("d"^2"P")/("dx"^2) = -4`

`therefore ("d"^2"P")/("dx"^2)` at (x = 60) = -4< 0

`therefore` P is maximum at x = 60.