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 4 km per hr, what was her boat speed in still water?

12 km/hour

Step-by-step explanation:

Given information: The current in that part of the river is 4 km per hr.

Speed of current = 4 km per hour

Let x be the speed of boat in still water.

Speed of boat in upstream = x-4 km per hour

Speed of boat in downstream = x+4 km per hour

Assume that the distance between Jane's initial position and Jane's favorite spot is D.

Jane took 20 min to drive her boat upstream to water-ski at her favorite spot.

For upstream,

           .... (1)

For downstream,

          ..... (2)

Equate (1) and (2) we get

Isolate variable terms.

Divide both sides by 10.

The value of x is 12. Therefore, the speed of boat in still water is 12 km/hour.