The answer is reciprocal.
The reciprocal of a number is any fraction flipped. The numerator becomes the denominator and the denominator becomes the numerator. If you are dealing with a whole number, it's reciprocal will have a one in the numerator.
Here are two examples:
[tex]7* \frac{1}{7} = \frac{7*1}{1*7} = \frac{7}{7}=1 [/tex]
[tex] \frac{5}{8} * \frac{8}{5} = \frac{5*8}{8*5} = \frac{40}{40}=1 [/tex]
