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Jane took 20 min to drive her boat upstream to​ water-ski at her favorite spot. Coming back later in the​ day, at the same boat​ speed, took her 10 min. If the current in that part of the river is 7 km per​ hr, what was her boat speed in still​ water?

Respuesta :

Answer: I might be wrong.

Step-by-step explanation:

To do 7 hm/h it'd be 4.34959835. She did it three times that time. 60/20 = 3 60/10 = 6. Three times to the location (13.04879505 mph) and six times back (26.0975901).

mhanifa

Answer:

  • The speed of the boat in still water was 21 km/h

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Given

  • The distance is d,
  • The speed of the boat in still water is s,
  • The speed of the current is 7 km/h,
  • Time upstream is 20 min or 20/60 hour,
  • Time downstream is 10 min or 10/60 hour.

Set equations for time

  • d / (s + 7) = 10/60   ⇒ d / (s + 7) = 1/6  ⇒ 6d = s + 7
  • d / (s - 7) = 20/60   ⇒ d / (s - 7) = 2/6  ⇒ 6d = 2(s - 7)

Eliminate d and solve for s

  • s + 7 = 2(s - 7)
  • s + 7 = 2s - 14
  • 2s - s = 7 + 14
  • s = 21

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