100
3 1/8 - 1 5/12 =
Why do you need to rename 3 1/8 when subtracting the above problem?
Because the fraction 1/8 is smaller than 5/12, so you have to rename the 3 as a 2.
Also, when you find common denominators, it is easy to see that 3/24 is smaller than 10/24. You cannot take a 10 from a 3, therefore you must regroup.