A person can row a distance of one km. upstream in ten minutes and downstream in four minutes. What is the speed of the stream? एक व्यक्ति एक किमी. ऊर्ध्वप्रवाह की दूरी दस मिनट में खे सकता है और अनुप्रवाह में चार मिनट में। प्रवाह की गति क्या है?
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5.6 km/hr./किमी./घंटा
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4.5 km/hr./किमी./घंटा
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4 km/hr./किमी./घंटा
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9 km/hr./किमी./घंटा
B
Correct answer
Explanation
Let boat speed be b km/hr and stream speed be s km/hr. Upstream speed = (b - s) = 1 km / (10/60) hr = 6 km/hr. Downstream speed = (b + s) = 1 km / (4/60) hr = 15 km/hr. Adding equations: 2b = 21, so b = 10.5 km/hr. Then s = 15 - 10.5 = 4.5 km/hr. The speed of the stream is 4.5 km/hr.