You open the electricity bill and the total looks wrong. Before you ring the supplier, you need to know what you are looking at. An electricity bill is not one number — it is a unit charge for the power you used, a standing charge for the days you were connected, and VAT on both. Today you pull a real-style bill apart line by line, then rebuild the total from the usage data yourself.
Three parts make up a typical electricity bill. Read the table, then look at the bill snapshot underneath — the same three parts, already worked out.
| Concept | Why it matters | Example |
|---|---|---|
| Unit charge — price per kWh of electricity used | This is the part that grows when you leave lights and heaters on | 742 kWh at 35.4c each |
| Standing charge — fixed amount per day for being on supply | You pay it even if the house is empty for a week | 61 days at 61.5c per day |
| VAT — percentage tax on the subtotal of both charges | VAT is charged on the combined subtotal, not only on the units | 9% of (unit charge + standing charge) |
Watch the bill below. Notice the subtotal row that appears just before VAT — that is the figure the percentage is applied to.
Three different bills, same rates. For each one, rebuild the total yourself: unit charge, standing charge, subtotal, VAT at 9%, then total to pay. Work the total out on paper first, then set the kWh and the days on the interactive and tap Check — it rebuilds every line and tells you whether the bill lands on the target. If your paper total and the screen disagree, find which line you differ on before moving on.
Work these three in order:
After each Check, say which part moved more than the original bill — the unit charge or the standing charge.
Now rebuild the original bill on paper without looking at the total. Work each line in order. Predict the answer before you check it.
Your Portfolio Build for today is an annotated electricity bill. Every line must be named, explained, and checked against the usage data so somebody else can follow your working.
Instructions: Use the sample figures from the lesson (742 kWh, 61 days, 35.4c/kWh, 61.5c/day, 9% VAT). For each line, write what it is and how the euro amount is worked out. Finish by checking that your total matches the bill total.
Work each row in order onto a fresh page in your Maths Portfolio. Show the working, not just the answer.
Write these down the page, leaving room under each for your answer:
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