Multiple choice

A boat takes 3 hours to travel from P to Q against the stream and Q to P along the stream. The distance between Q to P is 4 km. The speed of the stream is 1 km per hour. Find the speed of the boat in still water?

  1. 2

  2. 3

  3. 4

  4. 5
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let v be the boat's speed in still water. Downstream speed is v+1 km/h and upstream speed is v-1 km/h. The total time equation is 4/(v+1) + 4/(v-1) = 3 hours. Solving gives 8v = 3(v²-1), which yields v = 3 km/h. The negative solution is rejected as speed cannot be negative.

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