Comment
Share
Q)

# A group of 10 items has arithmatic mean 6. If the arithmatic mean of 4 of these remaining item is 7.5 then the mean of the remaining item is

$\begin {array} {1 1} (A)\;6.5 & \quad (B)\;5.5 \\ (C)\;4.5 & \quad (D)\;5.0 \end {array}$

Since $\large\frac{ \sum_{i=1}^{10} x_1}{10}=6$
$\Rightarrow \sum_{i=1}^{10}x_i=60$
$\large\frac{ \sum_{i=1}^{4} x_1}{10}=7.5$
$\sum_{i=1}^{4}x_i=30$
$\therefore \sum_{i=5}^{10}x_1=60-30$
$= 30$
$\Rightarrow$ Mean of remaining items = $\large\frac{30}{6}$
$= 5$