Working alone, Mary can pave a driveway in 5 hours and Hillary can pave the same driveway in 2 hours. When they work together, Mary thrives on teamwork so her rate increases by 33.33%, but Hillary becomes distracted and her rate decreases by 50%. If they both work together, how many hours will it take to pave the driveway?
Choose one
A) 2 hours	B) 4 hours	C) 5 hours	D) 6 hours	E) 7 hours
Initial working rates:   Mary = 1/5 per hour   Hillary = 1/2 per hour   Rate when working together:   Mary = 1/5 + (1/3*1/5) = 1/4 per hour   Hillary = 1/2 - (1/2*1/2) = 1/4 per hour   Together they work 1/4 + 1/4 = 1/2 per hour   So they will need 2 hours to complete the driveway. The correct answer is 2 hours.
<result>A</result>
Working alone, Mary can pave a driveway in 5 hours and Hillary can pave the same driveway in 2 hours. When they work together, Mary thrives on teamwork so her rate increases by 33.33%, but Hillary becomes distracted and her rate decreases by 50%. If they both work together, how many hours will it take to pave the driveway?