Given that cycling 1 mile indicates Alex is 1/3 of the way home, its safe to say that he needs to cycle 2/3 more to reach his destination.
We can look at it this way:
～ 1/3 = 1 mile
～ 2/3 = 1/3 + 1/3
ヽ 2/3 = 1 mile + 1 mile
ヽ 2/3 = 2 miles
～ 3/3 = 1/3 + 1/3 + 1/3
ヽ 3/3 = 1 mile + 1 mile + 1 mile
ヽ 3/3 = 3 miles total to reach home.
3/3 - 1/3 = 2/3
3 miles - 1 mile = 2 miles
As you can see, Alex will need to cycle two more miles in order to complete a full three thirds (3/3) of his journey back home.
Hope this helps! ッ
