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Asked by  | 24th Jan, 2012, 08:04: PM

Expert Answer:

Sn = 3n2 + 5n
Now a1 = S1 = 3+5 = 8
and, a2 = S2 - S1 =  12 + 10 - 8 = 14
therefore, d = a2 - a1 = 14 - 8 = 6
Now, am = 164
or, a + (m - 1)d = 164
or, 8 + (m - 1)6 = 164
or, (m - 1)6 = 156
or, m - 1 = 26
or, m = 27

Answered by  | 25th Jan, 2012, 09:41: AM

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