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# Arithmetic Series / Progressions - C1 Edexcel

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1. I am doing the June 2013 Edexcel C1 paper and keep making an error on question 7b)

7. A company, which is making 200 mobile phones each week, plans to increase its production. The number of mobile phones produced is to be increased by 20 each week from 200 in week 1 to 220 in week 2, to 240 in week 3 and so on, until it is producing 600 in week N.

(a) Find the value of N.(2) N = 21

The company then plans to continue to make 600 mobile phones each week.

(b) Find the total number of mobile phones that will be made in the first 52 weeks starting from and including week 1. (5)
I know the formula in n/2[2a+(n-1)d]

However I can never seem to get the correct answer. I do not know if I am just making a silly error and I have made it so many times on this question I cant seem to get the answer.

Any help would be appreciated.

Thank you

Tom
2. (Original post by Tommy1boy)
I am doing the June 2013 Edexcel C1 paper and keep making an error on question 7b)

7. A company, which is making 200 mobile phones each week, plans to increase its production. The number of mobile phones produced is to be increased by 20 each week from 200 in week 1 to 220 in week 2, to 240 in week 3 and so on, until it is producing 600 in week N.

(a) Find the value of N.(2) N = 21

The company then plans to continue to make 600 mobile phones each week.

(b) Find the total number of mobile phones that will be made in the first 52 weeks starting from and including week 1. (5)
I know the formula in n/2[2a+(n-1)d]

However I can never seem to get the correct answer. I do not know if I am just making a silly error and I have made it so many times on this question I cant seem to get the answer.

Any help would be appreciated.

Thank you

Tom
3. Do the n/2(2a+(n-1)d where n is 21 then add 31x600 since they're producing 600 phones every week for 31 weeks(52-21)

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4. (Original post by meowgoesthedog)
Do the n/2(2a+(n-1)d where n is 21 then add 31x600 since they're producing 600 phones every week for 31 weeks(52-21)

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Ah got it I knew it would be a silly mistake. I was doing 30*600
5. (Original post by Tommy1boy)
Ah got it I knew it would be a silly mistake. I was doing 30*600
Ahhh glad you finally got it then

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