Multiple choice

The speed of a boat in still water is 45 kmph. It covers a distance of 72 km downstream in 1 hour and 12 minutes. Find the time taken by the boat to cover the same distance upstream.

  1. 2 hours and 24 minutes

  2. 4 hours

  3. 5 hours and 15 minutes

  4. 1 hour and 42 minutes

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Downstream speed = 72 km / 1.2 hours = 60 kmph. Since downstream speed = boat speed + stream speed, 60 = 45 + stream speed, so stream speed = 15 kmph. Upstream speed = boat speed - stream speed = 45 - 15 = 30 kmph. Time taken = 72 km / 30 kmph = 2.4 hours, which is 2 hours and 24 minutes.

AI explanation

First, convert the downstream time to hours, which gives 1.2 hours. Using the speed formula, the downstream speed is 72 km divided by 1.2 hours, equaling 60 kmph. Since the downstream speed is the sum of the boat's speed in still water and the stream's speed, the stream's speed is 60 minus 45, or 15 kmph. The upstream speed is 45 minus 15, equaling 30 kmph. Finally, the time taken to travel 72 km upstream is 72 divided by 30, which equals 2.4 hours, or 2 hours and 24 minutes.

Keep practicing — related questions