Let the original price of ground nut oil be Rs x/kg.(case 1)
Then the new price will be x+5(case 2)
Qn of oil that can be purchased in case 1 is 180/x
Qn of oil that can be purchased in case 2 is 180/(x+5)
Acc to the given condition
180/(x+5) = 180/x - 0.5
This will result into a quadratic equation.
Solving the quadratic equation the valid answer will be , x=40.
Hence the original price of the oil will be Rs 40 per Kg.