Answer:
<u>39 percent</u> is increase in mileage.
Thus, the correct option is B. 39%.
Step-by-step explanation:
Given:
A runner increased her distance from 9 miles to 12.5 miles a week.
Now, to find percent increase in mileage.
Previous mileage = 9 miles.
Present mileage = 12.5 miles.
<em>Mileage increase = 12.5 - 9 = 3.5 miles.</em>
Now, to get the percent increase in mileage:
![\frac{Mileage\ increased}{previous\ mileage} \times 100](https://tex.z-dn.net/?f=%5Cfrac%7BMileage%5C%20increased%7D%7Bprevious%5C%20mileage%7D%20%5Ctimes%20100)
![=\frac{3.5}{9} \times 100](https://tex.z-dn.net/?f=%3D%5Cfrac%7B3.5%7D%7B9%7D%20%5Ctimes%20100)
![=\frac{350}{9}](https://tex.z-dn.net/?f=%3D%5Cfrac%7B350%7D%7B9%7D)
![=38.88\%.](https://tex.z-dn.net/?f=%3D38.88%5C%25.)
<u><em>Approximately the percent increase = 39%.</em></u>
Therefore, 39% is increase in mileage.
Thus, the correct option is B. 39%.