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

Answer 1

Let's assume the speed of the current is x mph.

When the boat is traveling with the current, the effective speed of the boat is 20 + x mph. Given that it takes 4 hours to cover a distance of 100 miles, we can set up the equation as follows:

100 = (20 + x) * 4

Dividing both sides by 4, we have:

25 = 20 + x

Subtracting 20 from both sides, we get:

x = 5 mph

When the boat is traveling against the current, the effective speed of the boat is 20 - x mph. Given that it takes 6 hours and 40 minutes (or 6.67 hours) to cover the same distance of 100 miles, we can set up another equation:

100 = (20 - x) * 6.67

Dividing both sides by 6.67, we have:

x = 20 - (100/6.67)

Simplifying, we get:

x ≈ 20 - 15 ≈ 5 mph

Therefore, the speed of the current is 5 mph.