How can I use Excel: Add a number from one cell to a continuous tally in another cell?

The previous answer is close to what I have. I would key all of your numbers into column A, i.e. 4,5,27,34,23,45; in the sequential cells A1 through A6 In cell B1, enter the formula =SUM(A1:A300). This will show you the total of the numbers in column A to be 138. When you put a 5 in cell A7, it will be added to the total number in B1.