Hobble20
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So I have question where the first term is 28 and increases by 3 for every term afterwards. There is a known total of 17000, how many terms until we get to that total. Please help
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Muttley79
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(Original post by Hobble20)
So I have question where the first term is 28 and increases by 3 for every term afterwards. There is a known total of 17000, how many terms until we get to that total. Please help
I would use the sum of a series formula and set it equal to 17 000 then solve. Post your working if you get stuck.
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Hobble20
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hi is stuck trying to work out how to redo the formula I’ve posted, if you can help it would be much appreciated
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the bear
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(Original post by Hobble20)
hi is stuck trying to work out how to redo the formula I’ve posted, if you can help it would be much appreciated
so you have the right formula.... you have values

Sn = 17000

a = 28

d = 3

put these in then you can work out n
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Muttley79
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(Original post by Hobble20)
hi is stuck trying to work out how to redo the formula I’ve posted, if you can help it would be much appreciated
Sorry - you need to use reply to quote me so I know you've responded.

Have you substituted in a = 28, d = 3 and sum = 17 000 - your photo only shows the formula
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Hobble20
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(Original post by Muttley79)
Sorry - you need to use reply to quote me so I know you've responded.

Have you substituted in a = 28, d = 3 and sum = 17 000 - your photo only shows the formula
Hi please forgive me, I’m new to this site as a user, please see photo
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Muttley79
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(Original post by Hobble20)
Hi please forgive me, I’m new to this site as a user, please see photo
Great - now expand and tidy up, post what you get
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Hobble20
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(Original post by Muttley79)
Great - now expand and tidy up, post what you get
Right this is where I get stuck, not sure how to alter the formula to get the value for “n”
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Muttley79
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(Original post by Hobble20)
Right this is where I get stuck, not sure how to alter the formula to get the value for “n”
OK can you expand and collect like terms?
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ghostwalker
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(Original post by Hobble20)
Right this is where I get stuck, not sure how to alter the formula to get the value for “n”
As Muttley79 said, expand and tidy up. Because you're going to have a term in n^2 there, making n the subject although doable isn't necessarily the way to go. You will have a quadratic in n, and use what ever means you've been taught to solve it.

HOWEVER, unless I made a slip, there is an error in the question. You cannot get a total of 17000 exactly. Please check the original question. I suspect it should say 170.
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