Problema Solution
The excursion boat travels 35k upstream and then back again in 4h 48min. If the speed of the boat in still water is 15km/h, what is the speed of the current?
Answer provided by our tutors
let
c = the speed of the current, c>=0
v = 15 km/h the speed of the boat in still water
d = 35 km the distance in one direction
t = 4 h 48 min = 4 48/60 h = 4.8 h the total time of the travel
the speed of the boat when moving upstream is: v - c
the speed of the boat when moving downstream is: v + c
since speed = distance/time => time = distance/speed
d/(v + c) + d/(v - c) = t
35/(15 + c) + 35/(15 - c) = 4.8
by solving the equation we find
c = 2.5 km/h
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the speed of the current is 2.5 km/h.