SOLUTION: After a rise in the price of petrol, the driven mileage dropped down by 6.7%. However the fuel cost increased by 4.5%. By what percentage did the petrol price rise?

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Question 954043: After a rise in the price of petrol, the
driven mileage dropped down by 6.7%. However the fuel
cost increased by 4.5%. By what percentage did the
petrol price rise?

Answer by Theo(13342)   (Show Source): You can put this solution on YOUR website!
if i understand the question correctly, i believe the increase in the cost of fuel per mile is 12%.

here's why:

at the current prices, people drove a total of y miles at a total fuel cost of x.

the average cost of fuel per mile is therefore x/y.

at the new cost of fuel per mile, people drove a total of (y - .067y) miles at a total fuel cost of (x + .045x) dollars.

the average cost of fuel per mile is therefore (x + .045x) / (y - .067y)

simplify the numerator and denominator and you get 1.045x / .933y.

simplify further to get the average cost of fuel per mile is 1.120042872*x/y

it looks very much like the total cost of fuel went up by 4.5% because the average cost of fuel per mile went up 12%.


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