Multiple choice

Azhar can row 9.333 kmph in still water and finds that it takes him thrice as much time to row up than as to row down the same distance in the river. The speed of the current of the river is

  1. 3.333 km/hr

  2. 3.111 km/hr

  3. 4.666 km/hr

  4. 4.5 km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let v be speed in still water (9.333) and c be current speed. Downstream speed = v + c, upstream = v - c. Time = Distance / Speed. Time_up = 3 * Time_down, so Distance / (v - c) = 3 * (Distance / (v + c)). Thus, v + c = 3(v - c), which means v + c = 3v - 3c, or 4c = 2v. c = v / 2 = 9.333 / 2 = 4.666.

AI explanation

Let the speed of the current be c; taking thrice the time to row up means the upstream speed is one-third of the downstream speed. We set 9.333 minus c equal to one-third of 9.333 plus c, which simplifies to 28 minus 3c equals 9.333 plus c. Solving this gives 4c equals 18.666, so the speed of the current is 4.666 km/hr.

Keep practicing — related questions