Every month a man consumes 25 kg rice and 9 kg wheat. The price of rice is 20% of the price of wheat and thus he spends total Rs. 350 on the rice and wheat per month. If the price of wheat is increased by 20% then what is the percentage reduction of rice consumption for the same expenditure of Rs. 350? Given that the price of rice and consumption of wheat is constant :

Answer: Option C

Let the price of wheat is x per kg. Then price of wheat will be 5x per kg.
Expenditure on rice = 25 × x = 25x
Expenditure of wheat = 9 × 5x = 45x
Total cost,
25x + 45x = 350
70x = 350
x = 5
Hence, price of Rice = Rs. 5 per kg.
Price of wheat = 25 per kg.
Now, price of wheat = 25 ---- 20% ↑----> Rs. 30 per kg.
Let the new amount of rice is N kg, then
N*5 + 9*30 = 350
N = 16 kg.
% decrease in the amount of rice
$$\begin{array}{rl}& =\frac{\left(25-16\right)\times 100}{25}\\ & =36\%\end{array}$$