Working alone, Mary can pave a driveway in 6 hours and Hillary can pave the same driveway in 6 hours. When they work together, Mary thrives on teamwork so her rate increases by 25%, but Hillary becomes distracted and her rate decreases by 20%. If they both work together, how many hours will it take to pave the driveway?  Options:
A) 3 hours B) 4 hours C) 5 hours D) 6 hours E) 7 hours
Initial working rates:   Mary = 1/6 per hour   Hillary = 1/6 per hour   Rate when working together:   Mary = 1/6+ (1/4*1/6) = 1/5 per hour   Hillary = 1/6 - (1/5*1/6) = 2/15 per hour   Together they work 1/5 + 2/15 = 1/3 per hour   So they will need 3 hours to complete the driveway. The correct answer is 3 hours.
<result>A</result>
Working alone, Mary can pave a driveway in 6 hours and Hillary can pave the same driveway in 6 hours. When they work together, Mary thrives on teamwork so her rate increases by 25%, but Hillary becomes distracted and her rate decreases by 20%. If they both work together, how many hours will it take to pave the driveway?