1. Select the cell where you want to display the date.
2. Type the formula =DATE(1900,1,1)+A1/86400 into the formula bar, where A1 is the cell containing the serial number.
3. Press Enter on your keyboard.

To apply this formula to multiple cells, you can use the Fill Handle. Here's how:

1. Select the cell containing the formula.
2. Hover your mouse over the bottom right corner of the cell until it turns into a small black cross.
3. Click and drag the cross down to the cells where you want to apply the formula.
4. Release the mouse button.

The formula should now be applied to all the selected cells, and the dates should be displayed in the format mm/dd/yyyy.