Household Bills (Junior Cert Mathematics): Revision Notes

Example Problem:

• The previous metre reading was 21,310 and the current reading is 21,836.
• The cost per unit of electricity is €0.15.
• There is a standing charge of €21.60.
• VAT of 13.5% is added to the total.

Step 1: Calculate the Units Used

• $Units Used = Current Reading - Previous Reading$
• Calculation: $21,836 - 21,310 = 526 \text{ units}$
• Explanation: Subtract the previous metre reading from the current reading to find out how many units of electricity you have used.

Step 2: Calculate the Cost of the Units Used

• Multiply the units used by the cost per unit:
• Calculation: $526 \times 0.15 = €78.90$
• Explanation: Multiply the number of units by the cost per unit to find out the cost of the electricity used.

Step 3: Add the Standing Charge

• Add the standing charge to the cost of the units used:
• Calculation: $€78.90 + €21.60 = €100.50$
• Explanation: The standing charge is a fixed amount that gets added to your bill regardless of how much electricity you use.

Step 4: Calculate the VAT

• Calculate the VAT by applying the VAT rate to the total before VAT:
• Calculation: $13.5\% \text{ of } €100.50 = \frac{13.5}{100} \times €100.50 = €13.57$
• Explanation: VAT is a tax added to the total cost. Multiply the total by the VAT rate (13.5% as a decimal is 0.135) to find out how much VAT is added.

Step 5: Calculate the Final Bill

• Add the VAT to the total before VAT to find the final amount you owe:
• Calculation: $€100.50 + €13.57 = €114.07$
• Explanation: Finally, add the VAT to the total to get your final bill amount.

Final Answer:

• The final electricity bill is €114.07.