An Olympic sprinter runs 200 meters in 20.1 seconds. Calculate the runner's speed in miles per hour.

Since their speed is 200meters/20.1seconds, we can try to multiply it out to get our answer. Using the identity property (we can multiply expressions by 1), we have 1 mile = 1609.34 meters, so we can multiply our expression by 1mile/1609.34meters (not we have the mile on the top to cross out the meters), ending up with 200*1mile / (20.1seconds*1609.34). To convert seconds into hours, we know that there are 3600 seconds in an hour, so we multiply it by 3600 seconds/1 hour (seconds on the top to cross out the seconds on the bottom), resulting in

200*3600*1mile / (20.1*1609.34*1 hour) = 22.25812788 miles/hour