Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 6-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water? (Please round your answer to one decimal place.)
To find the speed of Debbie's boat in still water, we need to set up an equation using the given information. Let's denote the speed of the boat in still water as "x" (in mph).
When Debbie is going upstream, the speed of the boat with the current is reduced by the 6-mph current, so her effective speed is (x - 6) mph. This speed allows her to travel the 5 miles upstream in 20 more minutes (or 1/3 hour) than her return trip.
Using the formula "distance = speed × time", we can set up the equation:
5 = (x - 6) × (1/3)
Now, let's solve for x:
Multiply both sides of the equation by 3 to get rid of the fraction:
15 = x - 6
Add 6 to both sides of the equation:
21 = x
So, the speed of Debbie's boat in still water is 21 mph when rounded to one decimal place.