Boat And Stream

Q 5: If Anil rows 10 km upstream in 2 hours and 30 km downstream in 2 hours, then the speed of the stream is A)4 km/hr B)2 km/hr C)8 km/hr D)5 km/hr Answer : Option D Explanation: Rate upstream = (10/2) km/hr =5 km/hr Rate downstream (30/2) km/hr = 15 km/hr. Speed of stream (1/2)(15 - 5)km/hr = 5 km/hr Q 6: . A Boy can row at 3 km/hr in still water. If the velocity of the current is 1 km/hr and it takes him 3 hour to row to a place and come back. how far is that place. A)3 km B)8 km C)4 km D)2 km Answer : Option C Explanation: Let the distance is x km Rate downstream = 3 + 1 = 4 km/hr Rate upstream = 3 - 1 = 2 km/hr then x/4 + x/2 = 3 [because distance/speed = time] => x + 2x = 12 => x = 12/3 = 4 km Q 7: The speed of a boat in still water in 18 km/hr and the rate of current is 2 km/hr. The distance travelled downstream in 24 minutes is: A)8 km B)6 km C)4 km D)10 km Answer : Option A Explanation: Speed downstream = (18 + 2) = 20 km/hr Time = 24 minutes =24/60 hour = 2/5 hour Distance travelled = Time × speed =(2/5)×20 = 8 km Q 8: A man can row upstream 18 km/hr and downstream 4 km/hr. Find the man rate in still water and rate of the stream. A)10 kmph,4 kmph B)11 kmph,7 kmph C)8 kmph,7 kmph D)12 kmph,5 kmph Answer : Option B Explanation: Please remember, If a is rate downstream and b is rate upstream Rate in still water = 1/2(a+b) Rate of current = 1/2(a-b) => Rate in still water = 1/2(18+4) = 11 kmph => Rate of current = 1/2(18-4) = 7 kmph

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