Question

The combined mean of three groups is $12$ and the combined mean of first two groups is $3$. If the first, second and third group have their mean as $2,3$ and $5$ times respectively, then the mean of third group is

• A. $10$
• B. $21$
• C. $12$
• D. $13$

Answer 1

The correct option is B $21$

Let in common no. in each group is $X$
Then Member of each group is $2X,3X$ and $5X$
Total of three group $=(2X+3X+5X)12=120X$(given mean of three group is 12)
And total of Two group $=(2X+3X)3=15X$ (given mean of two group is 3)
Then total of third group $=120X-15X=115X$
Mean of third group $=\frac{115X}{5X}=21$