Define variable

Question

a  boat travels 48 miles up a river in the same amount of time it takes to travel 72 miles down the same river. If the current is 3 miles per hour, what is the speed of the boat in still water? 

Answer 1

(Distance upstream/speed upstream) = (Distance downstream/speed downstream)

 

Upstream speed = speed in still water-speed of current

downstream speed = speed in still water+ speed of current

 

48/(x-3)  =  72/(x+3)

48(x+3)  =  72(x-3)  (Cross Multiplying)

 

48x+144 = 72x-216

72x-48x = 216+144

 

24x = 360

 

x = 15mph