SOLUTION: Find the sum of the first 25 terms of an arithmetic sequence whose third term is 24and whose common difference is 3.5. Write your answer as a whole number without a comma.

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Question 1003399: Find the sum of the first 25 terms of an arithmetic sequence whose third term is 24and whose common difference is 3.5.
Write your answer as a whole number without a comma.
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
+S%5Bn%5D the sum of n terms of an AP is

S%5Bn%5D+=+%28n%2F2%29%282a+%2B+%28n-1%29d%29


t%5B3%5D+=+a%2B2d}
d=3.5
24 = a+ 2*3.5
24 = a +7
a=17
a= 17 d= 3.5
S%5Bn%5D+=+%28n%2F2%29%282a+%2B+%28n-1%29d%29
S%5B25%5D+=+%2825%2F2%29%282%2A17+%2B+%2825-1%293.5%29

= 12.5 (34+84)
=12.5 *128
=1600
Sum of 25 terms is 1600