Problema Solution
a man travels 40km down a river and back in 6 hours. if speed of river current is 5km/hr. find speed of boat in still river
Answer provided by our tutors
let
d = 40 km the distance of the travel in one direction
t = 6 hr the time of the travel
c = 5 km/hr the speed of the current
v = the speed of the boat in still water, v>0
traveling downstream the speed of the boat is: v + c = v + 5
traveling upstream the speed of the boat is: v - c = v - 5
since speed = distance/time follows time = distance/speed:
d/(v + c) + d/(v - c) = t
40/(v + 5) + 40/(v - 5) = 6
by solving we find
v = 15 km/hr
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the speed of the boat in still river is 15 km/hr.