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    in the first month after opening, a mobile phone shop sold 180 phones. a model for future trading assumes that sales will increase by x phones per month for the next 35 months, so that (280+x) phomes will be sold in the ssecond month, (280+2x) in the third month and so on.

    using this modle with x=5, calculate:

    1) the number of phones sold in the 36th month
    2) the total number of phoes sold over the 36 months

    the shop sets a target of 17,000 phones to be sold over the 36 months

    using the same model,
    1) find the least value of x required to achieve this target.
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    (Original post by sammy33856)
    in the first month after opening, a mobile phone shop sold 180 phones. a model for future trading assumes that sales will increase by x phones per month for the next 35 months, so that (280+x) phomes will be sold in the ssecond month, (280+2x) in the third month and so on.

    using this modle with x=5, calculate:

    1) the number of phones sold in the 36th month
    2) the total number of phoes sold over the 36 months

    the shop sets a target of 17,000 phones to be sold over the 36 months

    using the same model,
    1) find the least value of x required to achieve this target.
    Okay I'm not just going to give you the answer but I'll help you do it.

    For questions 1 and 2 you will need the equations Un=a+(n-1)d and Sn=[n/2(2a+(n-1)d)]
    To work out the values of a and d you use the information given. A is the first term so that would be the number of phones sold in the first month so 180. D is the common difference, so is the difference between each term - as x is added between each term then d=x, and as x=5 for parts 1 and 2, d=5 as well.

    For the second question 1 you will again have to use the equation Sn=[n/2(2a+(n-1)d] but this time you will use it work out d which is the same value as x.
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    Moved to maths.
 
 
 
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