SOLUTION: Find the S20 if T3 = 19 and T8 = 44.

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Question 1109080: Find the S20 if T3 = 19 and T8 = 44.
Found 2 solutions by ikleyn, TeachMath:
Answer by ikleyn(53266)   (Show Source): You can put this solution on YOUR website!
.
There are 8-3 = 5 common differences between T3= 19  and  T8= 44, i.e.


5d = 44 - 19 = 25  ====>  d =  = 5.


Hence,   =  = 19-2*5 = 9.


Then  =  = 9 + 5*19 = 104.


It implies   =  =  = 113*10 = 1130.

Solved.

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There is a bunch of lessons on arithmetic progressions in this site:
    - Arithmetic progressions
    - The proofs of the formulas for arithmetic progressions
    - Problems on arithmetic progressions
    - Word problems on arithmetic progressions
    - Mathematical induction and arithmetic progressions
    - One characteristic property of arithmetic progressions
    - Solved problems on arithmetic progressions


Also,  you have this free of charge online textbook in ALGEBRA-II in this site
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Free of charge online textbook in ALGEBRA-II
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Answer by TeachMath(96)   (Show Source): You can put this solution on YOUR website!
Sum of 1st 20 terms = 1,130
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