Khanacademy tackles problems involving multiplicative inverse (i.e. taking the number one and dividing it by that number) and dividing rational numbers in its simplest form (lowest common form).
The multiplicative inverse of a number is where the number one is divided by the number itself. Five examples including whole numbers, fractions and negative fractions, and algebra are dealt with. The multiplicative inverse of 100 is one divided by 100. In the fraction two over eight, the multiplicative inverse is done just by switching the numbers from two over eight to eight over two which is the number four.
In dividing rational numbers involving fractions, the problem is re-written as a multiplication problem by switching the second fraction from top to bottom before simplifying it further. This works for problems involving negative fractions as well.