To simplify this expression, we can rewrite it as:

A = Σ (1/n * xn) from n=1 to 80

This is a summation notation where n represents the index of the term in the series.

Now, we can calculate the value of A by plugging in the values of n and x:

A = (1/1 * x21) + (1/2 * x22) + (1/3 * x23) + ... + (1/80 * x100)

A = x21 + x22/2 + x23/3 + ... + x100/80

Therefore, the simplified expression for A is the sum of x divided by the index n from 21 to 100.