Final answer:
Sergio's speed is found by calculating the ratio of distance to time. His running ratio in fractional form is 2.1/30 miles per minute, which equates to a speed of 4.2 miles per hour.
Step-by-step explanation:
The question asks to calculate Sergio's speed given that he runs 2.1 miles in 30 minutes. To find the speed, we can use the formula speed = distance/time. The ratio in fractional form would be 2.1 miles / 30 minutes or 2.1/30 miles per minute. To find his speed in miles per hour, we can convert the time to hours by dividing 30 minutes by 60 minutes (since there are 60 minutes in one hour), which gives us 0.5 hours. The speed is then 2.1 miles / 0.5 hours = 4.2 miles per hour.