Answer: 50 miles
Explanation:
Let the miles that she is trying to run by the end of the month be denoted by x.
Since she is 80% of the way to achieving her goal and she has already run 40 miles. This can be expressed as:
80% of x = 40
80/100 × x = 40
0.8x = 40
x = 40/0.8
x = 50
The miles that she is trying to run by the end of the month is 50 miles.