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A boat can go 5 km upstream and 7.5 km downstream in 45 minutes. It can also go 5 km downstream and 2.5 km upstream in 25 minutes. How much time (in minutes) will it take to go 6 km upstream?1. 242. 323. 364. 30 |
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Answer» Correct Answer - Option 3 : 36 Given: A boat goes 5 km upstream and 7.5 km downstream in 45 minutes Also, it goes 5 km downstream and 2.5 km upstream in 25 minutes Concept used: Upstream speed = Speed of the boat in still water - Speed of flow of the stream Downstream speed = Speed of the boat in still water + Speed of flow of the stream Calculation: Let the Downstream and Upstream speed be 'd' km/hr and 'u' km/hr respectively As per the question, 5/u + 7.5/d = 45/60 -----eq-n(1) 2.5/u + 5/d = 25/60 -----eq-n(2) Multiplying eq-n(2) by 2 and then subtracting eq-n(1) from (2), we get \({2.5 \over d}\) = \({5 \over 60}\) ⇒ d = 30 By putting the value of 'd' in any of the eq-n, we get the value of 'u' ⇒ u = 10 Now Time is taken to travel 6 km upstream = 6/10 hour or 36 minutes ∴ The time required to travel 6 km upstream is 36 minutes
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