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 :

Explanation:-

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 = [(25-16)*100]/25 = 36%.