Final answer:
Subtracting the extra 20 miles that Mike ran from Mike's total of 38 miles yields the distance Dan ran, which is 18 miles.
Step-by-step explanation:
Let's denote the number of miles Dan ran as D. According to the information provided, Mike ran 20 miles more than Dan. Therefore, Mike's distance is D + 20. The total distance Mike ran last week is given as 38 miles. So, we can set up an equation:
D + 20 = 38
Now, solve for D:
D = 38 - 20
D = 18
So, Dan ran 18 miles last week. To check, if Dan ran 18 miles, then Mike ran 18 + 20 = 38 miles, which matches the information given. Therefore, Dan ran 18 miles.