Problema Solution
A hydrofoil made the round trip of 120km between two islands in 3.5 hours of travel time. If the average speed going is 10km/h less than the average speed returning, find its speed
Answer provided by our tutors
Let
v = average speed going
v + 10 = average speed returning
t1 = the time needed for going
t2 = the time needed for returning
t1 + t2 = 3.5 hr
d = 120 km total distance traveled
Meaning the distance between the islands is d/2 = 120/2 = 60 km.
Since speed = distance/time we have distance = speed*time:
distance going + distance returning = d
v*t1 = 60 => t1 = 60/v
(v + 10)*t2 = 60 => t2=60/(v + 10)
Since t1 + t2 = 3.5 we have:
60/v + 60/(v + 10) = 3.5
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click here to see the equation solved for v
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v = 30 km/h
v + 10 = 30 + 10 = 40 km/h
The speed going was 30 km/h while the speed returning was 40 km/h.