 
                 
                InterviewSolution
 Saved Bookmarks
    				| 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/dx2 = 36 – 9x At x = 9, d2p/dx2 = 36 – 81 < 0 At x = 3, d2p/dx2 = 36 – 27 > 0 Therefore profit is maximum when x = 9. | |