The speed of the raft if the speed of the motorboat in still water is 3 km/h
Speed is defined as the ratio of the time distance travelled by the body to the time taken by the body to cover the distance.
Let the speed of the raft (current) - r
Speed of motorboat - 12 km/h
The distance between villages - is 44 km
Let the time spent by Aniskin - t
The time the thief was in travel = 2 hr 40 min + t = 2 40/60 + t = 3/8 + t
The distance the thief traveled = 44 - 27 = 17 km
We have the following equations:
r(8/3 + t) = 17
(12 - r)t = 27
Simplify the equations:
r(8/3 + t) = 17 ⇒ rt + 8/3r = 17
(12 - r)t = 27 ⇒ 12t - rt = 27
Add up the equations and solve for r:
rt + 8/3r + 12t - rt = 44
8/3r + 12t = 44
r = 16.5 - 4.5t
Substitute r into the second equation:
(12 - 16.5 + 4.5t)t = 27
4.5t² - 4.5t = 27
9t² - 9t - 54 = 0
Solving we get
t = 3 h
Find r:
r = 16.5 - 4.5*3 = 3 km/h
Therefore the speed of the raft if the speed of the motorboat in still water is 3 km/h
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