uptetd16p2 q148
- Option : D
- Explanation : (D) Let the sped of the stream be 'x' km/h
Speed of the motor boat in still water = 15 km/h
∴ Speed of the motor boat in upstream = (15 - x) km/h
Speed of the motor boat in downstream = (15 + x) km/h
Total time take by the motor boat = 5h
Distance covered by motor boat in upstream = 36 km
Hence, distance covered by motor boat in downstream = 36 km
5(15 + x) (15 - x) = 36[15 -x + 15 + x]
5[(15)2 -x2] = 36 (30) [∵ (a + b)(a - b) = a2 - b2]
(225 -x2) = 36 × 6 225 - 216 = x2
x 2 = 9
x = 3 km/h (speed of the stream)
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