Paul and Jack are 2 mechanics who work 8 hours per day changing oil in cars at The Oil Spot. If Paul can change oil in 2 cars per hour, and Jack can change oil in 3 cars per hour. What is the least number of cars per work day the 2 men can finish?  Choices:
A) 50  B) 40  C) 35  D) 10  E) 90

Rationale: the proportion equation can be used . let x = number cars and c = least number of cars per day the 2 men can finish ( c = x / ( 8 hours ) , p = cars per hour paul can change , and j = cars per hour jack can change . note : 8 hours = a work day p + j = c ( 2 cars / hour ) + ( 3 cars / hour ) = x / ( 8 hours ) proportion : 2 / 1 + 3 / 1 / = x / 300 x = 8 ( 2 + 3 ) = 40 . at least 40 cars per work day . answer is b
Answer: B