College math

Question

On a weekend? outing, Carlos rents a motorboat for 10 hours to travel down the river and back. The rental operator tells him to go for 4hours? downstream, leaving 6 hours to return upstream.If the river current flows at a speed of 4 mph, how fast must Carlos travel in order to return in 10 Hours?

Answer 1

Hi Chelsea,

 

Let X = the speed of the boat in still water

 

Then the boat goes X + 4 mph downstream X - 4 mph upstream

 

Distance = rate x time

 

Time downstream is 4 hours and time upstream is 6 hours

The distance downstream is the same as the distance upstream

 

So, (X + 4) x 4 = (X -4) x 6

 

4X + 16 = 6X - 24

 

40 = 2X

 

X = 20 mph

 

Dan