Today you will

• write formulas that start with an equals sign
• use SUM to add up costs and AVERAGE to find a typical cost
• add a live Total and Average cost to {{code:05_project_budget}}

If you don't have {{code:05_project_budget}} yet, you can use today's practice sheet.

Warm-up

Your project has twelve costs, and one price changes. How long would it take to add them all up again by hand?

A formula tells the spreadsheet to work something out. It always starts with {{code:=}}.

A cell reference is a cell's address, like {{code:C2}}. Use it instead of typing the number, so the answer updates when the number changes.

A range is a block of cells. {{code:C2:C6}} means every cell from C2 down to C6.

Example

{{formula:=SUM(C2:C6)}} adds up every cost from row 2 to row 6. If you forget the {{code:=}}, the sheet just shows your typing as words.

You will make a practice sheet for a phone-case stall at a local market, then add SUM and AVERAGE to it. Follow the steps in the box below. When the steps ask for the headings and costs, type them from this box.

Common snags

• If your formula doesn't calculate, check that it starts with {{code:=}}.
• If the total doesn't change when you edit a cost, you typed a number by mistake. Click the cell, check the formula bar, and type the SUM formula again.
• If the total is wrong or shows an error, check the range. It must cover every cost and stop above the Total cell.