SOLUTION: i need to find the sum of the first nth terms of the arithmetric series. 3+8+13+18+23 n=20 Sn=366

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Question 79546: i need to find the sum of the first nth terms of the arithmetric series.
3+8+13+18+23
n=20
Sn=366
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
i need to find the sum of the first nth terms of the arithmetric series.
3+8+13+18+23
n=20
Sn=366
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It is a arithmetic sequence with a(1)=3 and d=5
The 20th terms is a(20)=3+19*5=98
The sum of the 1st 20 terms is (20/2)(3+98)=1010
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FYI: Noice the the sum of the 20 terms is the average of
the 1st an last terms times 20 as you can see here:
20[(3+98)/2]
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Cheers,
Stan H.