On in-line skates, bradley skates 4 miles in 20 minutes. at this speed, how long would it take him to skate the entire length of a 12-mile bike path?

1 hour (60 minutes)

Step-by-step explanation:

If his speed remains the same, that means that this is a linear relationship.  y increases at the same rate as x increases.  Direct variation and all of that.  Because this is a linear relationship, it can be solved using proportions.  Set up the given info in a ratio with miles on the top and minutes on the bottom:

Now we want to know how long (unknown number of minutes) it will take him to go 12 miles.  Keep miles with miles and minutes with minutes:

=

We can cross multiply now to get 4x = 12(20) and 4x = 240.  That means that x=60.  It will take him 60 minutes (1 hour) to go 12 miles.