The 9th term of an AP is 52 while the 12 term is 70 find the sum of the 20 terms.

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    posted by Abu

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    posted by Damon
  3. a+8d = 52
    a+11d = 70
    Now find a and d, and then
    S20 = 20/2 (2a+19d)

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    posted by oobleck

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