A car dealership has 40 cars on the lot, 10% of which are silver. If the dealership receives a new shipment of 80 cars, 25% of which are not silver, what percentage of total number of cars are silver? Choose one.
A) 15 %  B) 18 %  C) 20 %  D) 21 %  E) 22 %

Rationale: the number of silver cars is 0.1 * 40 + 0.25 * 80 = 24 the percentage of cars which are silver is 24 / 120 = 20 % the answer is c .
Answer: C