Statistics And Probability Question 521
Question: The number of observations in a group is 40. If the average of first 10 is 4.5 and that of the remaining 30 is 3.5, then the average of the whole group is
[AMU 1992; DCE 1996]
Options:
A) $ \frac{1}{5} $
B) $ \frac{15}{4} $
C) 4
D) 8
Show Answer
Answer:
Correct Answer: B
Solution:
$ \frac{x_1+x_2+…..+x_{10}}{10}=4.5 $
Þ $ x_1+x_2+…..+x_{10}=45 $ and $ \frac{x_{11}+x_{12}+…..+x_{40}}{30}=3.5 $
Þ $ x_{11}+x_{12}+…..+x_{40}=105 $ \ $ x_1+x_2+…..+x_{40}=150 $ \ $ \frac{x_1+x_2+…..+x_{40}}{40}=\frac{150}{40} $ $ =\frac{15}{4} $ .
BETA
