I am trying to calculate an average on excell.  I want to know if there is a
way that i can put a number in a cell, put another number in the cell and
have excell create an average of those two numbers
i will have two cells - one that i put the numbers into and the other that i
want to create a average of all of those numbers

say i put 4 in a cell, i want to find a way to write over that number ex. by
putting in a 8 and have excell create a running average of those two numbers.
I want to do this however for many than 2 numbers and somehow weight the
average.  

Thanks