The price at which $x$ units can be sold is $p = 80 - 4x$ rupees each. What is the marginal revenue when 5 units are sold?

Explanation

1. 01

   $R(x) = x(80 - 4x) = 80x - 4x^{2}$, so $MR = 80 - 8x$.

2. 02

   At $x = 5$: $80 - 40 = 40$ rupees.