Multiple choice

If a boat goes $7$ km upstream in $42$ minutes and the speed of the stream is $3$ kmph, then the speed of boat in still water is:

  1. $4.2$ km/hr
  2. $9$ km/hr
  3. $13$ km/hr
  4. $21$ km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Upstream speed = 7 km / (42/60) hr = 7 / 0.7 = 10 km/h. Upstream speed = Boat speed - Stream speed. 10 = Boat speed - 3, so Boat speed = 13 km/h.

AI explanation

The upstream speed is distance divided by time, which is 7 km divided by 42/60 hours, equaling 10 km/hr. Using the upstream speed formula, the speed of the boat in still water is the upstream speed plus the speed of the stream, giving 10 + 3 = 13 km/hr. The result is 13 km/hr.

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