What is a radian? How do you find linear velocity?

Explain in your own words what it means for an angle to have measure 1 radian.

Using a narrative of each step you are taking, explain thoroughly how you solve this problem:   If you are riding a bike and your front sprocket (the one with the pedals) has 40 teeth and the rear sprocket (the one connected to your back tire) has 20 teeth, and you are pedaling at a rate of 50 rpm, how fast (in miles per hour) are you going if your bike has 27 inch diameter wheels?