SOLUTION: How to you find the fourth term of an arithmetic series, given a1 = 20 and the sum (S subroot 10) = 335?

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Question 456892: How to you find the fourth term of an arithmetic series, given a1 = 20 and the sum (S subroot 10) = 335?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!

==> S%5B10%5D+=+335+=+%2810%2F2%29%2A%282%2A20+%2B+9%2Ad%29
==> 335 = 5(40 + 9d)
==> 67 = 40 + 9d
==> 27 = 9d
==> d = 3.
==> a%5B4%5D+=+a%5B1%5D+%2B+%28n-1%29d+=+20+%2B+3%2A3+=+29