A man can row 9 km/h in still water and he finds that it takes him twice as much time to row up than to row down the same distance. Find the speed of the current. MCQ with Answer and Explanation
A man can row 9 km/h in still water and he finds that it takes him twice as much time to row up than to row down the same distance. Find the speed of the current.
A. 4 km/h
B. 2 km/h
C. 3 km/h
D. 4.5 km/h
Answer: Option C
Solution (By JKSSB Mock Tests)
Let speed of current be c. Downstream speed = 9 + c, Upstream speed = 9 - c. Since time is twice for upstream, speed must be half: 9 - c = (9 + c) / 2 => 18 - 2c = 9 + c => 3c = 9 => c = 3 km/h.
Explanation:
New speed = 4/5 of usual speed => New time = 5/4 of usual time. Difference = 1/4 of usual time = 10 minutes. Usual time = 10 * 4 = 40 minutes.
A commuter departs from outpost A at 5:00 AM at 25 km/h. Another starts from A at 7:00 AM at 35 km/h tracking along the same direction corridor. At what distance away from A will they intercept?
Explanation:
By 7:00 AM, the first commuter tracks for 2 hours, covering 25 * 2 = 50 km. Relative speed index = 35 - 25 = 10 km/h. Time to intercept = 50 / 10 = 5 hours. Distance path from point A = Speed of second commuter * Intercept Time = 35 * 5 = 175 km.
Explanation:
New speed = 7/9 of usual speed => New time = 9/7 of usual time. Difference = 2/7 of usual time = 16 minutes. 1/7 of usual time = 8 minutes => Usual time = 56 minutes.
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