Quantitative Aptitude Ques 555
Question: The average of the first nine integral multiples of 3 is
Options:
A) 12
B) 15
C) 18
D) 21
Show Answer
Answer:
Correct Answer: B
Solution:
- By using arithmetic series Sum of first 9 integral multiples of 3 $ S _{n}=\frac{n}{2}[2a+(n-1),d] $ where, $ n=9, $ $ a=3 $ and $ d=3 $
$ \therefore $ $ S _{n}=\frac{9}{2}[2\times 3+(9-1),3]=\frac{9}{2}\times 30=135 $
$ \therefore $ Average $ =\frac{135}{9}=15 $ Alternate Method Average of n multiples of any number $ =\frac{Number\times (n+1)}{2}=\frac{3\times (9+1)}{2}=\frac{3\times 10}{2}=15 $
BETA
