Question

A motorboat with the current went 72 mi in 4 hours. Against the current, the motorboat could go
only 40 mi in the same amount of time. Find the rate of the motorboat in calm water.

Answer 1

Answer:

14 mph

Step-by-step explanation:

Speed of boat in calm water = x

Speed of current = y

Speed of boat with the current = 72 mi / 4 hr = 18 mph

Speed of boat against current = 40 mi / 4 hr = 10 mph

x + y = 18

x - y = 10

2x = 28

x = 14

Answer: 14 mph

Answer 2

Answer:

14 m/hr

Step-by-step explanation:

72 m / 4 hr = 18 m/hr

40 m / 4 hr = 10 m/hr

still water speed =  (18+ 10 )/2 = 14 m/hr

 current speed   (14 -x) 4 = 40

                       x = current speed = 4 m/hr