Hi there!
To find other possible combinations, we can see which other numbers add up to 3:
1 + 2 = 3
Andrea could have hiked one 1 mile trail and one 2 mile trail.
2 1/2 + 1/2 = 3
Andrea could have hiked a 2 1/2 mile trail and a 1/2 mile trail.
Hope this helps!