Cross-reducing is a short cut you can take to reduce before you even multiply the fractions. It is often easier to cross-reduce before multiplying than to reduce after multiplying. Consider this example:
We can reduce after multiplying like this: 1 5 5 1 --- * --- = --- = --- 5 6 30 6 Or we can cross-reduce before multiplying like this: 151 --- * --- = ---56 6 Since the fives cancel each other out, we just multiply 1/1 and 1/6 which gets us 1/6.
1 6 1
--- * --- = ---
6 7 7
Since the sixes cancel each other out, we just
multiply 1/1 and 1/7 and get 1/7.
Now you get to try a few for yourself.