Determine the average speed of the current in a river if a boat moves at 20 miles/hour in still water and takes 3 hours to travel 78 miles downstream

The speed of the current in a river if a boat moves at 20 miles/hour in still water is 6 miles per hour

Solution:

Formula for downstream:

If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr, then:  

Speed downstream = (u + v) km/hr

Given that boat moves at 20 miles/hour in still water

Speed of boat in still water = 20 miles per hour

The boat takes 3 hours to travel 78 miles downstream

Let us find the speed of downstream

The formula for speed is given as:

Thus speed downstream is 26 miles per hour

Let "v" be the speed of current

Let "u" be the speed in still water

Given, u = 20 miles per hour

Then by above mentioned formula,

Speed downstream = (u + v) miles per hour

26 = 20 + v

v = 26 - 20

v = 6

Thus speed of current in river is 6 miles per hour