We need a common denominator before we subtract. Both numbers go into 8. 5/8 stays as 5/8 and 1/2 becomes 4/8
Now we can subtract: 5/8 - 4/8
All we have to do is subtract the numerators (5 - 4) and keep the same denominator.
5 - 4 = 1
The answer is 1/8.