Let's agree that 2.5 miles : 18 minutes is the ratio between the amount of distance and the amount of time spent running. If we spent 2x as many minutes running, Shelly would run 5 miles. In the same context, let's find the amount of distance covered in 18 minutes.
18 × (60/18) = 60
We multiply 60/18 because 60/18 = 60 × (1/18), and the (1/18) cancels with the 18 so we are left with the numerator, 60.
2.5 : 18
Now, we have to multiply 60/18 on both sides!
2.5 × (60/18) : 18 × (60/18) = 60
2.5 × (60/18) = 8 and 1/3 miles
