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1). 1 hour2). 1 hour and 15 minutes3). 1 hour and 30 minutes4). 2 hours |
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Answer» Speed of each BOAT in still water = 8 km/hr Suppose the speed of STREAM is v km/hr. ⇒ Speed of boat that goes upstream = (8 – v) km/hr And, Speed of boat that goes downstream = (8 + v) km/hr Suppose the boats meet after T hours. We know, Distance = Speed × Time ⇒ Distance COVERED by boat moving upstream = (8 - v) km/hr × T hr = (8 - v)T km ⇒ Distance covered by boat moving downstream = (8 + v) km/hr × T hr = (8 + v)T km Now, total distance covered by boats should be EQUAL to 20 km. ⇒ (8 – v)T + (8 + v)T = 20 ⇒ 16T = 20 ⇒ T = 1.25 hours = 1 hour + (0.25 × 60 MINUTES) = 1 hour and 15 minutes ∴ Time taken for the boats to meet = 1 hour and 15 minutes |
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