Tea worth Rs. 126 per kg and Rs. 135 per kg are mixed with a third variety in the ratio 1 : 1 : 2. If the mixture is worth Rs. 153 per kg, the price of the third variety per kg will be:

Answer: Option C

Since first and second varieties are mixed in equal proportions.
So, their average price
$$\begin{array}{rl}& =\text{Rs}\text{.}\left(\frac{126+135}{2}\right)\\ & =\text{Rs}\text{.}130.50\end{array}$$
So, the mixture is formed by mixing two varieties, one at Rs. 130.50 per kg and the other at say, Rs. x per kg in the ratio 2 : 2, i.e., 1 : 1. We have to find x.
By the rule of alligation, we have:

$$\begin{array}{rl}& \therefore \frac{x-153}{22.50}=1\\ & \Rightarrow x-153=22.50\\ & \Rightarrow x=175.50\end{array}$$