Browse Questions

# Choose the correct answer in the total revenue in Rupees received from the sale of $x$ units of a product is given by $Rx = 3x^2 +36x + 5$. The marginal revenue, when $x = 15$ is

$(A)\; 116 \qquad (B)\; 96 \qquad (C)\; 90 \qquad (D)\; 126$

Toolbox:
• If $y=f(x)$,then $\large\frac{dy}{dx}$ measures the rate of change of $y$ w.r.t $x$.
• $\big(\large\frac{dy}{dx}\big)_{x=x_0}$ represents the rate of change of $y$ w.r.t $x$ at $x=x_0$
Step 1:
Since the marginal revenue is the rate of change of total revenue w.r.t the number of units sold.
Given : $R(x)=3x^2+36x+5$
Therefore $\large\frac{dR}{dx}=\frac{d}{dx}$$(3x^2+36x+5) \qquad\qquad\;\;\;\;=6x+36 Step 2: When x=15 \large\frac{dR}{dx}$$=6\times 15+36$
$\quad\;\;=Rs.126$
Hence $D$ is the correct option.