Cost Price = \(120 \times 60\)
\(SP_{S} = y \times 60 \times \Big( 1 + \dfrac{y}{100} \Big)\)
\(SP_{J} = (120 - y) \times 60 \times \Big( 1 + \dfrac{100 - y}{100} \Big) = (120 - y) \times 60 \times \Big( 2 - \dfrac{y}{100} \Big)\)
\(\text{Profit} = SP - CP = y \times 60 \times \Big( 1 + \dfrac{y}{100} \Big) + (120 - y) \times 60 \times \Big( 2 - \dfrac{y}{100} \Big) - 120 \times 60 \qquad \to (1)\)
\(= 60y + (60\times \dfrac{y^2}{100}) +(120\times 60 \times 2) - (120 \times 60 \times \dfrac{y}{100}) - (2\times 60\times y) + (60 \times \dfrac{y^2}{100}) - (120\times 60)\)
\(= 1.2 y^2 - 132 y + 7200 = y^2 - 110y +6000\) (This is the final equation which is after simplifying the equation (1))
For a quadratic equation, \(ax^2 + bx + c\) the minimum value occur at \(x = -\frac{b}{2a} \)
Therefore, minimum value is \(y = -\dfrac{(-110)}{2\times 1} = 55\)
Subtitute, \(y = 55\) at equation (1):
Profit = \(55 \times 60 \times \Big( 1 + \dfrac{55}{100} \Big) + (120 - 55) \times 60 \times \Big( 2 - \dfrac{55}{100} \Big) - 120 \times 60 = 5115 + 5655 - 7200 = 3570\)
ANS C