Which fraction do you invert when you are dividing fractions?

When dividing fractions, you invert the second fraction.

To divide fractions, you need to multiply the first fraction by the reciprocal of the second fraction. The reciprocal of a fraction is obtained by interchanging the numerator and the denominator. So, to find the reciprocal of a fraction, you invert it by swapping the numerator and the denominator.