Multiple choice

A motor boat covers a certain distance downstream in a river in five hours. It covers the same distance upstream in five hours and a half. The speed of the water is $1.5$km.hr. The speed of the boat in still water is ___________.

  1. $30$km/hr
  2. $30.5$km/hr
  3. $31.5$km/hr
  4. $20$km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let boat speed be v and stream speed be 1.5. Downstream: d = 5(v + 1.5). Upstream: d = 5.5(v - 1.5). Equating: 5v + 7.5 = 5.5v - 8.25 => 0.5v = 15.75 => v = 31.5.

AI explanation

Let the speed of the boat in still water be x km/hr. Since the distance covered downstream and upstream is the same, we equate the distances using the formula distance equals speed multiplied by time. This gives us 5(x + 1.5) = 5.5(x - 1.5). Expanding both sides yields 5x + 7.5 = 5.5x - 8.25, which simplifies to 0.5x = 15.75, meaning the speed of the boat in still water is 31.5 km/hr.

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