A means arrangement. Arranging is like queuing. Objects are ordered.
C means combination, just like fried rice with eggs and fried rice with eggs. These objects are disordered.
Because of its different meanings, the calculation method is close to:
A(x,y)=y! /(y-x)!
C(x,y)=y! /(y-x)! *x!
Where y> = X.
A deep understanding of concepts is a good way to solve scientific problems logically. What is depth? It depends on your own understanding.