The price of milk was first increased by 10% and then decreased by 20%. What is the net percentage change in final price of milk?

7.5 10 12 15

12

Formulae of net effect: x + y + \(\frac{xy }{100 }\) 10 - 20 + \(\frac{-200 }{100 }\) = -10 - 2 = -12%  i.e. decrease by 12%