Can someone please help me out with the following problem?
If the price of petrol increases by 25%, by how much must a user cut down his consumption so that his expenditure on petrol remains constant?
Maybe follow this line of thought.
Lets say $10 used to buy you 8 litres of petrol.
Now with a 25% increase implies $12.50 will now buy you 8 litres of petrol. You need to know how many litres to buy at the new price such that you are still only spending $10.
So 8 litres at $12.50 is $1.56 a litre.
So you need to know $1.56 by X (litres) = $10