Multiple choice

A boat goes 36 km downstream in 3 hours and returns the same distance upstream in 6 hours. If the speed of the stream increases by 2 km/h, how much time will it take to return upstream over the same distance?

  1. 9 hours

  2. 7 hours

  3. 8 hours

  4. 10 hours

  5. 12 hours
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Downstream speed = 36/3 = 12 km/h. Upstream speed = 36/6 = 6 km/h. Stream speed = (12-6)/2 = 3 km/h. Boat speed = 9 km/h. New stream speed = 3+2 = 5 km/h. New upstream speed = 9-5 = 4 km/h. Time = 36/4 = 9 hours.

AI explanation

Calculate the initial upstream speed by dividing 36 km by 6 hours, resulting in 6 km/h. Increasing the stream's speed by 2 km/h reduces the boat's new upstream speed to 4 km/h. The time required to return the same distance upstream is now 36 km divided by 4 km/h, which equals 9 hours.

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