The speed of the current is 5 mph and this can be determined by using the concept of upstream and downstream.
Given :
A motorboat takes 40 minutes to travel 20 miles downstream.
When the boat is going downstream current helps the boat and hinders when the boat is going up.
So, the boat downstream speed is given by:
[tex]\rm s = \dfrac{20}{40}=0.5\;miles \;per\;minute=30\;mph[/tex]
The speed of the boat going upstream is:
[tex]\rm s = \dfrac{20}{60}=\dfrac{1}{3}\;miles \;per\;minute = 20\;mph[/tex]
So, the speed of the current adds when the boat is going downstream and subtracted when the boat is going upstream.
Let the speed of the current be 'c' then:
s + c = 30
s = 30 - c --- (1)
s - c = 20 --- (2)
Substitute the value of 's' inequation (2).
30 - c - c = 20
2c = 10
c = 5 mph
So, the speed of the current is 5 mph.
For more information, refer to the link given below:
https://brainly.com/question/23774048
