Sequence And Series Question 90
Question: The number $ 111…………..1 $ (91 times) is a
Options:
A) Even number
B) Prime number
C) Not prime
D) None of these
Show Answer
Answer:
Correct Answer: C
Solution:
$ S=1+10+10^{2}+……+10^{90} $ (91 terms) $ =\frac{1.(10^{91}-1)}{10-1}=\frac{{{(10^{13})}^{7}}-1}{10^{13}-1}\times \frac{10^{13}-1}{10-1} $ $ =[{{(10^{13})}^{6}}+{{(10^{13})}^{5}}+{{(10^{13})}^{4}}+……1] $ $ (10^{12}+10^{11}+……+1) $ It is the product of two integers and hence not prime.
BETA
