You cannot reduce a-2.
It means reduce 1 to 1/2, reduce 4 to 2. Half it.
When you reduce four tents by two you get two. 4-2=2
It depends on what you wish to reduce it to.
There's no way to reduce age in Fable 2.
0.1111
Divide by 2
2
2/7
2/3
1/2
1/2
42