Multiple choice

A motorboat covers a distance of 102 km downstream in 2 hours 50 minutes. If the speed of current is 1/2 of the speed of boat, then in how much time will it cover the distance of 162 km upstream?

  1. 12.5 hr

  2. 12.7 hr

  3. 11.5 hr

  4. 13.5 hr

  5. 13.8 hr
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Downstream speed = 102 km / (170/60 hr) = 102 * 60 / 170 = 36 km/h. Let boat speed be B and current speed be C. B + C = 36. Since C = B/2, B + B/2 = 36, so 1.5B = 36, B = 24 km/h, C = 12 km/h. Upstream speed = B - C = 24 - 12 = 12 km/h. Time = 162 / 12 = 13.5 hours.

AI explanation

The downstream speed is 102 km divided by 17/6 hours (since 2 hours 50 minutes is 2 and 5/6 hours), yielding 36 km/hr. Using the downstream speed formula, if the boat's speed is 2x and the current's speed is x, then 3x equals 36, making the boat's speed 24 km/hr and the current's speed 12 km/hr. The upstream speed is the difference between the boat's speed and the current's speed, which is 12 km/hr. The time to cover 162 km upstream is 162 km divided by 12 km/hr, resulting in 13.5 hours.

Keep practicing — related questions