A person can row 10 km/h in still water. If it takes him exactly twice as long to row upstream as to row downstream over the same stretch, find the speed of the current. MCQ with Answer and Explanation
A person can row 10 km/h in still water. If it takes him exactly twice as long to row upstream as to row downstream over the same stretch, find the speed of the current.
A. 3.33 km/h
B. 3.03 km/h
C. 4.00 km/h
D. 3.66 km/h
Answer: Option A
Solution (By JKSSB Mock Tests)
Let speed of current be c km/h. Downstream speed = 10 + c, Upstream speed = 10 - c. Given: 2 * (10 - c) = 10 + c => 20 - 2c = 10 + c => 3c = 10 => c = 10/3 = 3.33 km/h.
Explanation:
Ratio of speeds A:B = 6:7, so ratio of times taken A:B = 7:6. Given 7 parts = 2.1 hours for car A => 1 part = 0.3 hours. Time taken by car B = 6 parts = 6 * 0.3 = 1.8 hours.
A man walks from his residence to a focal point at 4 km/h and arrives 10 minutes late. If he increases his speed to 5 km/h, he arrives 2 minutes early. Find the distance.
Explanation:
Let total distance be 100 km. First part = 40 km; Time = 40 / 20 = 2 hours. Second part = 60 km; Time = 60 / 30 = 2 hours. Total distance = 100 km, Total time = 4 hours. Average speed = 100 / 4 = 25 km/h.
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