To multiply or Divide fractions, you need to simplify it sometime during or when you get the final answer, but it is probably easier to simplify during the process of getting your final answer. Ex: 3/10 x 5/12, you could simplify by doing the cross-division thing where the three would go into the twelve and the five would go into the 10, so you get 1/2 x 1/4, which equals 1/8. Or dividing: ex: 5/18 รท 15/6. You would first have to reciprocate the divisor, and it becomes multiplication like so: 5/18 x 6/15. It would be the same process as above, which would give 1/3 x 1/3 which equals 1/9. The same philosophies can be applied to rational expressions. For example: