Multiple choice

A boat travels upstream from A to B and back from B to A in 5 hours. The speed of the boat in still water is 8 km/hour and the speed of the current is 4 km/hour. Then, the distance from A to B is

  1. 9 km

  2. 10 km

  3. 12 km

  4. 15 km
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Upstream speed = 8-4 = 4 km/hr. Downstream speed = 8+4 = 12 km/hr. Let distance be D. D/4 + D/12 = 5. (3D+D)/12 = 5. 4D = 60. D = 15.

AI explanation

The downstream speed is 8 km/hour plus 4 km/hour, which equals 12 km/hour. The upstream speed is 8 km/hour minus 4 km/hour, which equals 4 km/hour. Let the distance be D km; using the formula Time = Distance / Speed, the equation is (D/12) + (D/4) = 5. Solving this yields D + 3D = 60, so 4D = 60, meaning D equals 15 km. The result is 15 km.

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