Question

The speed of a boat in still water is 10 km/hr. The boat travels 24 km upstream, turns

around and comes back the same route. The entire trip takes 5 hours, What is the
speed of the current?

Answer 1

rate of the current = 2 km/hr

Explanation:

d = rt

Let c = rate of the current

Rate of boat downstream = 10 + c

Time going downstream = 24/(10 + c)

Rate of boat upstream = 10 - c

Time going upstream = 24/(10 - c)

Since the total time is 5 hr, then

24/(10 + c) + 24/(10 - c) = 5

24(10 - c) + 24(10 + c) = 5(10 + c)(10 - c)

240 - 24c + 240 + 24c = 500 - 5c^2

480 = 500 - 5c^2

5c^2 = 20

c^2 = 4

c = 2 or -2

Since a rate cannot be negative, the rate of the current = 2 km/hr