Suppose the speed that they paddled was x mi/h speed of current was 3 mi/h speed of moving upstream (x-3) mi/h speed of moving downstream (x+3) mi/h one way distance=24/2=12 miles time taken to move up stream: 12/(x-3) hr time taken to move downstream 12/(x+3) hr total time they paddled: (8:30 a.m -4:00 p.m)-(1:30) =7.5-1.5 =7 hours thus 12/(x-3)+12/(x+3)=7 solving for x we get: =24x/(x-3)(x+3) 24x/(x^2-9)=7 thus x=5.1695~5.2 hours x=5.2 mi/hr thus time taken to paddle downstream: 12/(5.2-3) =5 5/11 hours =5 3/11 hours =5 hours 27 minutes ~5 hours 25 minutes
