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A river flows at 4 km/hr. The speed of a boat in downstream is thrice the speed of that boat in upstream. Find out the speed of the boat in still water?1. 8 km/hr2. 4 km/hr3. 6 km/hr4. 12 km/hr |
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Answer» Correct Answer - Option 1 : 8 km/hr Given: Speed of river flow = 4 km/hr Speed of boat in downstream = 3 × Speed of boat in upstream Concept used: Speed of boat in downstream = Speed of boat in still water + speed of river flow Speed of boat in upstream = Speed of boat in still water - speed of river flow Calculation: Let the speed of boat in still water be 'x' km/hr Let the speed of boat in downstream and upstream be 'd' km/hr and 'u' km/hr respectively Then, as per question d = 3 × u ⇒ x + 4 = 3×(x - 4) ⇒ x + 4 = 3x - 12 ⇒ x = 8 ∴ Speed of boat in still water is 8 km/hr. |
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