Alg 2

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What is the sum of a 12-term arithmetic sequence where the last term is 13 and the common difference is -10?

  • Alg 2 -

    Schuyler, the sum of the 12 term aritmetic progression is 816

  • Alg 2 -

    Schuyler, in order to solve your problem I had to turn it around (Gloria Estefan?). You said the last term was 13...I made it the first term. You said the common difference was a -10...I made it a +10.
    Now I had to find the last term so I used this formula: L=a+(n-1)d so 13+(12-1)10
    L=123
    Then I used this formula:
    Sn=n/2(a+L)
    Sn=12/2(13+123)
    Sn=6 Times 136
    Sn=816

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