The ratio of buses to cars on River Road is 1 to 3. If there are 20 fewer buses than cars on River Road, how many cars are on River Road? Choose one
A) 100 B) 120 C) 140 D) 30 E) 150

Rationale: "b / c = 1 / 3 c - b = 20 . . . . . . . . . > b = c - 20 ( c - 20 ) / c = 1 / 3 testing answers . clearly eliminate abce put c = 30 . . . . . . . . . > ( 30 - 20 ) / 30 = 10 / 30 = 1 / 3 answer : d"
Answer: D