SOLUTION: Need help please.. Thanks How many of this succession terms -12,-7,-2,3,8...need to be sum so the total will be 105 ?

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Question 1008776: Need help please.. Thanks
How many of this succession terms -12,-7,-2,3,8...need to be sum so the total will be 105 ?
Found 2 solutions by farohw, MathTherapy:
Answer by farohw(175) About Me  (Show Source):
You can put this solution on YOUR website!

In this arithmetic sequence, each term is added by 5 which is the common difference. To obtain a sum of 105:

-12, -7, -2, 3, 8, 13, 18, 23, 28, 33

If you add these ten terms, your sum will be 105.


Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!

Need help please.. Thanks
How many of this succession terms -12,-7,-2,3,8...need to be sum so the total will be 105 ?
highlight_green%28matrix%281%2C4%2CThe%2C+1%5E%28st%29%2C10%2C+terms%29%29

Use the formula for the sum of the terms of an AP: S%5Bn%5D+=+%28n%2F2%29%282a%5B1%5D+%2B+%28n+-+1%29d%29%29, with:

S%5Bn%5D being the sum of the series

n  being the number of terms (UNKNOWN)

a%5B1%5D being the 1st term

d  being the common difference between the terms

Find n.