BRAINLIEST! ASAP! A boat travelling at top speed upstream moves at 15km/hr. When it travels downstream, again at top speed< it moves at 25km/hr. What is the boat's top speed in still water?

  20 km/hr

Step-by-step explanation:

The boat's still-water speed is the average of its speeds against and with the current:

  (15 +25)/2 = 20 . . . km/hr

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If you want to write equations, you can let b and c represent the speeds of the boat and current in km/hr.

  b - c = 15 . . . . upstream speed

  b + c = 25 . . . . downstream speed

Add these two equations, and you get ...

  (b -c) +(b +c) = (15) +(25)

  2b = 40

  b = 20 . . . . divide by 2

The speed of the boat in still water is 20 km/hr.

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step-by-step explanatio89