Q. A group of 10 items has arithmetic mean 6. If the arithmetic mean of 4 of these items is 7.5, then the mean of the remaining items is
A) 6.5
B) 5.5
C) 4.5
D) 5.0
Explanation
(d)
Given that, $n_{1} = 4,\ \ \overline{x} = 7.5,\ \ n_{1} + n_{2} = 10,\ \ \overline{x} = 6$
$\therefore\ \ \ 6 = \frac{4 \times 7.5 + 6 \times {\overline{x}}_{2}}{10}$
$\Rightarrow \ \ \ 60 = 30 + 6{\overline{x}}_{2}$
$\Rightarrow \ \ {\overline{x}}_{2} = \frac{30}{6} = 5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.