The speed of a boat in still water is 20 mph. It travels from one pier to another with the current in 4 hours and back against the current in 6 hours and 40 min

Question

If the distance between piers is 100 miles, what is the speed of the current?

Answer 1

d = rt  since the distance traveled is the same then rt = rt.  Let x = current

 

4(20+x) = 20/3(20-x)  and simplify

 

80 + 4x = 400/3 - (20/3)x

 

(32/3)x = 160/3

 

x = 5

Answer 2

Let's assume speed of current is X mph.

 

Time taken to travel from one pier to another with the current = 100/(20+x) h

But the time taken to travel from one pier to another with the current is already given to you that is 4 hours.

 

So, you must have

 

4=100/(20+x)

 

80+4x=100

4x=20

x=5.

 

So, the speed of the current is 5 miles per hour.