He rode 2 7/20 miles.
How to do it:
1. Find common denominator. In this case, it is 20 because it is the lowest number both denominators can go into.
2. Change denominators into 20.
3. Multiply the numerator by how much the denominator went in the common denominator. In this case, 5 goes into 20 four times, so 3 x 4 = 12, so 1 3/5 is now 1 12/20. Do the same with 1 3/4 and you get 1 15/20
4. Add numerators and whole numbers.
5. The answer should be 1 27/20
6. Now you simplify it into 2 7/20