SOLUTION: The cost of petrol increased by 15% one week but fell back to the original price the next week. By what percentage did the cost of petrol fall in the second week?

Question 1020249: The cost of petrol increased by 15% one week but fell back to the original price the next week.
By what percentage did the cost of petrol fall in the second week?
Answer by Fombitz(32388) (Show Source): You can put this solution on YOUR website!
Let's say the price starts at X.

During the 15% increase,

During the unknown decrease,
"Y is the percentage decrease you're looking for"
Make that new price equal to the original price, X.

You can divide X out of both sides.
Now solve for Y.

Subtract 1.15 from both sides

Multiply both sides by 100 and divide both sides by 1.15.

About a 13% decrease.

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