Write the Word or Phrase That Best Completes Each Statement $$r _ { 1 }$$

Short Answer

Write the word or phrase that best completes each statement or answers the question.
Provide the missing information.
-Consider a set of n elements of which one element is repeated $$r _ { 1 }$$ times. Then the number of
permutations of the elements of the set is given by $\frac { \square } { \square } \text {. }$