Dharmendra can row 80 km upstream and 110 km downstream in 13 hours. Also, he can row 60 km upstream and 88 km downstream in 10 hours. What is the speed (in km/h) of the current?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 6.
Let the upstream speed be U and downstream speed be D.
80/U + 110/D = 13 ...(i)
Also, 60/U + 88/D = 10 ...(ii)
Multiplying equation (i) by 3 and equation (ii) by 4 and subtracting equation (i) from equation (ii),
⇒ 352/D - 330/D = 40 - 39
⇒ D = 22 km/h
Now, 80/U + 110/22 = 13
⇒ 80/U = 8
⇒ U = 10 km/h
Now, speed of stream = (D - U)/2
⇒ (22 - 10)/2 = 6 km/h