Just. Another Summation
Algebra
Level
4
\(\sum_{n=4}^{20} \frac{(n-4)!}{(n)!}\)
If the result of the summation above can be written in form \(\frac{a}{b}\) for \(a\) and \(b\) are positive, coprime integers, find \(a + b\)
by
Muhammad Rizki Fadillah