a reduction in the price of petrol by 10% enables a motorist to buy five gallons more for $180.Find the original price of petrol.

Let's say price of petrol per gallon = $x and number of gallons bought earlier for same net price be y x(y) = 180 ---(1) and with a discount of 10%, he/ she can get 5 gallons more ((90/100)x)(y+5) = 180 ---(2), on solving 1 and 2, we get original price to be $4. Cheers.