SOLUTION: Find S[5] for the arithmetic sequence with a[3]=39 and a[5] =61

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Question 835036: Find S[5] for the arithmetic sequence with
a[3]=39 and a[5] =61
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Find S[5] for the arithmetic sequence with
a[3]=39 and a[5] =61
----
a(3) = a + 2d = 39
a(5) = a + 4d = 61
----
Subtract to solve for "d":
2d = 22
d = 11
-------
Solve for "a":
a + 2d = 39
a = 39-2*11
a = 17
--------
To find S(5)
S(n) = (n/2)(a+L)
S(5) = (5/2)(17+61) = 5(39) = 195
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Cheers,
Stan H.