SOLUTION: find the sum of the following sequence: 3, 7, 11, 15,..., 79?

Question 1075976: find the sum of the following sequence: 3, 7, 11, 15,..., 79?
Found 2 solutions by josgarithmetic, stanbon:
Answer by josgarithmetic(39618) (Show Source): You can put this solution on YOUR website!

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Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
find the sum of the following sequence: 3, 7, 11, 15,..., 79?
Determine "n"::
79 = 3 + (n-1)4
76 = (n-1)4
n-1 = 19
n = 20
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Sum = (n/2)(a(1) + a(20))
Sum = 10(3+79) = 10*82 = 820
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Cheers,
Stan H.
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