Question:
A reduction of 20% in the price of sugar enables a housewife to purchase 6 kg more for Rs. 240. What is original price per kg of sugar.

Option A):
Rs. 6 per Kg
Option B):
Rs. 5 per Kg
Option C):
Rs. 8 per Kg
Option D):
Rs. 10 per Kg

Correct Answer is Option D):
Rs. 10 per Kg

Explanation:
It is based on inverse proportion or product constancy concept. Reduction in price 20% amount of sugar will increase 25%.
It means,
25% = 6 Kg. So,
Initially, total Sugar = 6*4 = 24Kg. Thus,
Original price of the sugar was,
240/24 = Rs. 10 per kg.

Note:
Let initial price of 100 kg Sugar was Rs. 100.
Now, 20% decrease in rate then rate of 100 kg sugar would be Rs. 80.
So,
Rs. 80 = 100 kg sugar.
Rs. 1 = 100/80 kg sugar.
Rs. 100 = (100 *100)/80 = 125 Kg sugar.
Increment in sugar = 25 kg.
% increment = (25*100)/100 = 25%.
Means 20% rate decrease, 25% of consumption increase.