Determine the speed of a motor boat in still water and the speed of the river current, if it takes 3 hours to travel a distance of 45 mi upstream and 2 hours to travel 50 mi downstream.

Answer 1

3(x-w) = 45 = 3x -3w

2(x+w) = 50 = 2x +2w

multiply 1st by 2 and 2nd by 3 to get

6x + 6w = 150

6x -6w = 90 add to get

12 x = 240

x = 20 mph

subtract to get

12w =60

w = 5 mph

upstream speed = 15mph downstream 25 mph

3 hours upstream means 3x15 = 45 miles

2 hours downstream means 2 x 25 = 50 miles