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  • Level: GCSE
  • Subject: Maths
  • Word count: 1266

Gary’s Car Sales

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Gary’s Car Sales


The aim of this assignment is to find out what factors affect the second hand price of cars.


I think the second hand price of a car mainly depends upon two of the three factors of age, mileage and engine size, but also other smaller factors such as central locking and air conditioning etc. For this assignment however we were only asked to concentrate on information that we were given such as the age, make of car, mileage and engine size.

To test if my theory is correct I will make an equation that will tell me the second hand price of a car if I input certain characteristics like the age and mileage. To do this, I will first have to plot scattergraphs and create equations from them first before making the overall equation for everything.


To find out which of the factors made the most difference, I made scattergraphs on each factor against the second hand price, with a line of best fit to help show correlation’s and to help create a formula.

...read more.


 (All cars NP added together)    (No. Of cars in Gary’s garage)

                379520                        /                    36                         =10542.22 (2 d.p)

 This makes this straight-line equation complete

Y=MX+C becomes 4456.39=714.28*5.8 + 10542


SHP = G1A + NP(new price)

Next was the theory that the mileage may affect the 2nd hand price

The graph here shows all the cars mileage plotted against the second hand price.

Once again you can clearly see the negative correlation, showing that when the mileage increases, the second hand price decreases.

The marks ringed in red do not add to the correlation pattern. As with most scattergraphs, there are always a few that do not follow the trend of the others

The equation for this graph is basically the same as the other

Y = MX + C becomes 4456.39=225.17*55195(the average mileage) + 10542


SHP =  G2M + NP

(M being for the mileage)

The next factor to consider was the Engine size

From the graph opposite, you can clearly see that there is very little correlation at all in the SHP against the engine size and therefore doesn’t affect the second hand price enough to be able to make an equation from.

...read more.


I am 70% out which, once again is not what we want.

The closest of these was the first test, where the formula was only about 6% out.

We can see that there is not enough information in the formula to give exact results, but we still may be able to get closer results by adding more to this equation.


My aim of this investigation was to find out what the second hand price of a car depends upon in Gary’s garage.

My theory at the beginning was that the two main factors of Age and Mileage would have the greatest influence and the engine size would have a slightly less influence, but still add in some way to the coat of the SHP.

I have drawn scattergraphs and noted correlation’s and have found out that yes, my theory was correct, as shown in my scattergraphs. The Mileage and Age affect the 2nd hand price greatly whereas the engine size does not show any affect, but it would change the second hand price in some way.

Although I did find a formula, it is nowhere near as accurate as it could have been, had I been given the right information, suc

...read more.

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