Calculating simple expressions
In a spreadsheet a workbook consists of sheets. The columns of a sheet are named with letters (A to XFD, 16 384 in all) and the rows with numbers (1 to 1 048 576); a cell address is built from the column letter and the row number, for example C45. A formula always begins with the “=” sign, so that Excel understands the entry as an expression to calculate, not as text. The operations are + (add), – (subtract), * (multiply), / (divide) and ^ (power). Powers are done first, then multiplication and division, and addition and subtraction last; brackets change the order. The cell shows the result, while the formula itself is in the formula bar; the file extension is .xlsx. If a formula cannot be calculated, the cell shows an error value: #DIV/0! (division by zero), #NAME? (name not recognised), #VALUE! (wrong type of value), #REF! (reference to a cell that does not exist); the #### sign appears when a number does not fit in the column. This lesson was written for Excel 2010, but formulas work the same way in current Excel, LibreOffice Calc and Google Sheets.
“Predict the error”: the teacher writes three formulas: =5/0, ="Hello"+1 and =ABC(2). Students guess which error value each gives, and then the result is checked on the computer.