This question is related to rate time distance

Question

Jane took 30 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 20 min. If the current in that part of the river is 7 km per hour, what was her boat speed in still water?

Answer 1

Keissa, this one is slightly more difficult than the other.

 

We still have d = rt. Since the distances are the same, but the current either takes away from or adds to the rate of the boat...

 

30(r - 7) = 20(r + 7)

30r - 210 = 20r + 140

10r = 350

r = 35

 

The boat's speed in still water is 35 mph.