If a boat travels 18 km more in downstream than in
upstream in 3 hr. and if the speed of the Boat in still
water is 20 km/hr. find the distance travelled by boat
in downstream in 4 hr. ?
(a) 86 (b) 92 (c) 68
(d) 96 (e) None of these
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Let the speed of the motor boat in still water = u km/h
Let the speed of tte stream = v km/h
Speed of the boat down stream = (u + v) km/h
Speed of the boat up stream = (u - v) km/h
Distance travelled downstream by in 3 hours = (3 h) × [(u + v) Ikm/h] = 3 (u +v) km ————(1)
Dtance travelled upstream in 3 hours = (3 h) × [(u - v) km/h] = 3 (u - v) km ——————————-(2)
According to the statement of the questions;
3 × [ (u + v) - (u - v)] = 18 km
3 [ u + v - u + v] = 18 km
6 v = 18 km
v = 3 km/h
The speed of the stream = 3 km/h
Speed of the boat downstream = 20 km/h + 3 km/h = 23 km/h
The distance travelled downstream by the boat in 4 h = 4 h × ( 23) km/h = 92 km.
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