Nita blends two varieties of tea one costing Rs. 180 per kg and another costing Rs. 200 per kg in the ratio 5 : 3. If she sells the blended variety at Rs. 210 per kg then her gain is = ?

Answer: Option C

Let 5 kg of cheaper be mixed with 3 kg of dearer.
Then,
Total CP = Rs. (180 x 5 + 200 x 3) = Rs. 1500
Total SP = Rs. (210 x 8) = Rs. 1680
$$\begin{array}{rl}& \text{Gain}\%=\left(\frac{180}{1500}\times 100\right)\%\\ & =12\%\end{array}$$