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A boat covered 20 km downstream and 28 km upstream. The speed of boat in still water is 7 km/hr and speed of stream is 3 km/hr. Find the time taken to complete 20 km downstream and 28 km upstream.1. 9 hours2. 8 hours3. 6 hours4. 10 hours |
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Answer» Correct Answer - Option 1 : 9 hours Given: Distance covered downstream = 20 km Distance covered upstream = 28 km Speed of boat in still water = 7 km/hr Speed of stream = 3 km/hr Concept used: Downstream speed = Speed of boat in still water + Speed of stream Upstream speed = Speed of boat in still water – Speed of stream Calculation: Downstream speed = (7 + 3) km/hr ⇒ 10 km/hr Upstream speed = (7 – 3) km/hr ⇒ 4 km/hr Time taken to cover 20 km downstream = 20/10 hours ⇒ 2 hours Time taken to cover 28 km upstream = 28/4 hours ⇒ 7 hours Total time taken to complete the whole journey = (2 + 7) hours ⇒ 9 hours ∴ The time taken to complete the whole journey is 9 hours |
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