I have seen a lot of kids quickly pass off their 2’s, 5’s, and 10’s. These tables have an obvious pattern and are much easier to learn. Then there is a serious slow down as kids hit the 3’s, 4’s, and 6’s. By the time they get to the 7’s, 8’s, and 9’s they’ve decided that multiplication is way too hard, and math isn’t their thing.
Subtracting fractions is similar to adding fractions. Most of the work involves the denominator. If the denominators of the two fractions are already the same, much of the work is done. Simply subtract the two numerators to get the answer fraction using the same denominator, and then reduce and make a proper fraction.