Open a blank Microsoft Excel spreadsheet. Often you can access Excel as an icon on your Start menu. If you do not see it listed there, then from the Start menu click "All Programs," "Microsoft Office" and "Microsoft Office Excel." You will see a blank spreadsheet open.
Click on cell "A1." You will be typing text in this cell. If the cell is too small for text, then grab the vertical bar on the "A" column header, and drag it to the right. You want enough space in your cell to write a sentence.
Write your "clues" to help your children figure out the birthday of the person in question. For example, you might write the following: "Sarah is 10 years old and was born in the month of March on the 11th day. Today's date is March 11, 2011. What is Sarah's birthday?"
Allow your children to practice typing their equation to answer your question in B1. In this case, your child will write "2011" in "B1" and "10" in "B2." In "B3," your child will type the following Excel formula: "=INT(A1-A2)" without the quotes. The answer that will appear is 2001. Therefore, Sarah was born in 2001.
Repeat hypothetical problems as in steps 3 and 4 for practice.