1.

If MR and MC denote the marginal revenue and marginal cost and MR – MC = 36x – 3x2 – 81, then the maximum profit at x is equal to _______ (a) 3 (b) 6 (c) 9 (d) 5

Answer»

(c) 9 

The maximum profit occurs when MR – MC = 0 

⇒ 36x – 3x2 – 81 = 0 

⇒ x2 – 12x + 27 = 0 

⇒ (x – 9)(x – 3) = 0 

⇒ x = 9, 3

Now = dp/dx 36x2 – 3x – 81 ⇒ d2p/dx= 36 – 9x 

At x = 9, d2p/dx= 36 – 81 < 0 

At x = 3, d2p/dx= 36 – 27 > 0 

Therefore profit is maximum when x = 9.



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