Sequence And Series Question 425
Question: If the sum of the series $ 54+51+48+…………. $ is 513, then the number of terms are
[Roorkee 1970]
Options:
18
20
17
D) None of these
Show Answer
Answer:
Correct Answer: A
Solution:
According to the condition
$ \Rightarrow $ $ 513=\frac{n}{2}{ 2\times 54+(n-1)(-3) } $
$ \Rightarrow $ $ a_1+a_{24}=75 $
$ \Rightarrow $ $ 3n^{2}-111n+1026=0 $
$ \Rightarrow $ $ n=2 $ Hence $ n=18 $ .
BETA
