To divide by a fraction you invert the fraction and multiply. There are many reasons why you might need to divide by a fraction. If you have a question like: if I have 6 apples and that's 2/3 of the apples my friend has, how many apples does my friend have? To get the answer you have to divide 6 by 2/3, which is 6*3/2=9, because 2/3 of 9 is 6.