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How do you work out a car's fuel consumption and the cost of running it?

Calculating fuel consumption (miles per gallon or litres per 100 km), the cost of a journey's fuel, and the main running costs of a vehicle.

A CCEA GCSE Motor Vehicle and Road User Studies answer on calculating fuel consumption (mpg or litres per 100 km), the fuel cost of a journey, and the running costs of owning a vehicle.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
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What this dot point is asking

CCEA wants you to calculate a car's fuel consumption (in miles per gallon or litres per 100 km), work out the fuel cost of a journey, and know the main running costs of a vehicle. The specimen paper directly asks you to "calculate the vehicle's average fuel consumption", so this is core motoring mathematics.

The answer

Fuel consumption

Fuel consumption measures how far a car goes on a given amount of fuel.

A higher mpg is more economical; for litres per 100 km, a lower figure is more economical (it uses less fuel for the same distance).

Fuel cost of a journey

To find the cost of fuel for a journey:

  1. Find the fuel used = distance ÷ fuel consumption.
  2. Multiply by the price per unit of fuel.

fuel cost=distanceconsumption×price per unit.\text{fuel cost} = \frac{\text{distance}}{\text{consumption}} \times \text{price per unit}.

The running costs of a vehicle

The fuel is only part of the cost of running a car. Costs are usually grouped as:

Converting between gallons and litres

Fuel is sold in litres but consumption is often quoted in miles per gallon. The conversion is about 1 gallon ≈ 4.5 litres. So a 40-litre tank holds about 40÷4.5≈8.940 \div 4.5 \approx 8.9 gallons, and a car that uses 9 gallons uses about 9×4.5≈40.59 \times 4.5 \approx 40.5 litres. Always check which unit a question uses before you start.

Worked example: comparing two cars

Worked example: the fuel cost of a journey in litres

Examples in context

Example 1. The economical choice. A car doing 60 mpg uses far less fuel over a year than one doing 30 mpg, which can outweigh a higher purchase price.

Example 2. Depreciation surprise. A new car can lose a large share of its value in the first few years, so depreciation often costs more than the fuel.

Try this

Q1. A car travels 240 miles on 6 gallons. What is its mpg? [1 mark]

  • Cue. 240÷6=40240 \div 6 = 40 mpg.

Q2. Name one standing (fixed) cost of running a car. [1 mark]

  • Cue. Any one of: insurance, vehicle tax, depreciation, MOT.

Q3. A car does 30 mpg. How many gallons are needed for a 90-mile trip? [2 marks]

  • Cue. 90÷30=390 \div 30 = 3 gallons.

Exam-style practice questions

Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

CCEA style3 marksA car uses 30 litres of fuel to travel 360 km. Calculate its average fuel consumption in litres per 100 km.
Show worked answer →

Fuel consumption in litres per 100 km =litres useddistance in km×100= \dfrac{\text{litres used}}{\text{distance in km}} \times 100.

=30360×100=8.33 litres per 100 km (to 2 d.p.).= \frac{30}{360} \times 100 = 8.33\ \text{litres per 100 km (to 2 d.p.)}.

Markers reward dividing litres by distance and multiplying by 100, giving about 8.3 litres per 100 km.

CCEA style4 marksA car does 40 miles per gallon. A driver makes a 120-mile journey. (a) How many gallons of fuel are used? (b) If fuel costs GBP 6.00 per gallon, what is the cost of the fuel for the journey?
Show worked answer →

(a) Gallons used =distancemiles per gallon=12040=3 gallons.= \dfrac{\text{distance}}{\text{miles per gallon}} = \dfrac{120}{40} = 3\ \text{gallons}.

(b) Cost =gallons×price per gallon=3×6.00=GBP 18.00.= \text{gallons} \times \text{price per gallon} = 3 \times 6.00 = \text{GBP } 18.00.

Markers reward distance ÷ mpg = 3 gallons, then gallons × price = GBP 18.00.

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