Sequence And Series Question 507
Question: If sum of $ n $ terms of an A.P. is $ 3n^{2}+5n $ and $ T_{m}=164 $ then $ m= $
[RPET 1991, 95; DCE 1999]
Options:
A) 26
B) 27
C) 28
D) None of these
Show Answer
Answer:
Correct Answer: B
Solution:
Obviously $ 164=(3m^{2}+5m)-{3{{(m-1)}^{2}}+5(m-1)} $ $ =(3m^{2}+5m)-3m^{2}+6m-3-5m+5 $
$ \Rightarrow $ $ 164=6m+2 $
$ \Rightarrow $ $ m=27 $ .
BETA
