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# Maths - Sequences and Series watch

1. 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.
2. (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.

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.
3. Moved to maths.

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