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  • Level: GCSE
  • Subject: Maths
  • Word count: 7547

For this task we were required to create a model that can be used to economise on my quarterly household electricity bill.

Extracts from this document...


Coursework modelling 1B - Write Up

For this task we were required to create a model that can be used to economise on my quarterly household electricity bill. My family quarterly electricity bill may be too high. I need to try and devise a method to bring the bill down to an acceptable level. There are lots of aspects of an electricity model that need to be known. Some of the important ones are:

  • Unit- these are kilowatt-hours, which are the amount of hours an appliance uses multiplied by the kilowatts the appliance has.
  • Tariff- the rate at which a company charges a unit.
  • Two-tier tariff- this can also be called a split rate. There are two different costs per unit. There is usually a cost for the first units up to a certain value, sometimes known as a split value, and a different cost per unit for any units after the split value. My bill uses a two-tier tariff. I have named it a split rate model throughout this write – up.
  • Value added tax (VAT)- this is usually a percentage and is added on to a price.
  • Standing charge- a value of money that is added onto a price. It is normally a value without percentages, and is added on to a price just for using a supplier.  

There are many different types of bills. The bills are usually paid quarterly. There is a standard model, which is simply calculated by multiplying the unit amount by the cost per unit. A unit can also be called a kilowatt- hour (kWhr). By multiplying the kilowatt of an electrical appliance by the time the appliance is used, in hours, we can obtain a value which is measured in kWHr. For example, a 0.1kW bulb is switched on for 20 hours.

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After working out the IF formulae, I then had to type in the data for the cost before and after the split value. I then worked out a total cost for the units by multiplying the cost of the first 182 units by the first IF formulae cell, and then adding this to the cost of the units after 182 units multiplied by the second IF cell. This gave a total cost for the units. All that needed to be worked out after that was the VAT amount and the standing charge. However, my bill didn’t have a standing charge, so I typed zero pounds, so that if a standing charge is introduced to an npower bill, the model can apply it to the total cost. VAT for my bill was at 5%. To work out the VAT, I multiplied the cell containing the 5% data by the total of the standing charge and the cost of the units. I then used a SUM formula to calculate the total of the bill. The formula totalled the VAT cost, the total cost for the units, and the standing charge, if there is one. For the total cost of the units I used “custom number formatting.” This meant that I was able to write “TOTAL COST FOR WEEK IS” and then the total cost, in one cell, and the spreadsheet treats it as if it is just the formula for the total cost. I did after the formula worked out the total cost. I then highlighted the result and went on to format cells. I then went on to the number tab and clicked on custom. I typed in what I wanted before the result, and placed speech marks either side of the text. The number was referred to as ‘general.

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Overall, I have learnt a lot of things from my ‘what if’ questions. My predictions weren’t much off. VAT was usually the cause of this. I created a chart after finding out results to my ‘what if’ questions so that it can easily be seen which prices are more expensive than others. The chart is easy to understand and can be interpreted by most people. The chart shows that economy 7 split rate (British Gas) was the most expensive by a considerable amount. This is probably because of the split value that British Gas use. Economy 7 split rate would be more efficient to my family if we use more units of electricity. Otherwise the best model to use for my family is the standard model. Economy 7 could be better for my family, but only if I make changes to the way I use my electricity. It would be more efficient if more of our electrical units could be used at night. Therefore these units would be priced at a low cost. It is possible for my family to adjust and change our electrical usage. I think my mother could start to iron her clothes more during the night. My dad could start vacuuming at night so that these units could be priced lower. I could also make my family have a suitable night period, to work with my electrical usage.

A chart is given below to show how my ‘what if’ questions compare to my normal model.


I created this chart so that it can be seen easily which ‘what if’ is cheaper than my normal model. It can be seen from my chart that economy 7 split rate (British Gas) is the most expensive for me. There are many changes my family can make to ensure the cheapest bill possible. Using less T.V. for example is a great possibility.

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