Question

A set of $7$ observations has mean $10$ and another set of $3$ observations has mean $5.$ The mean of combined set is:

• A. $15$
• B. $10$
• C. $8.5$
• D. $7.5$

Answer 1

Answer: (C)

$8.5$

Mean of 7 observations $=10$

Sum of 7 observations $=10\times 7=70$

Mean of 3 observations $=5$

Sum of 3 observations $=3\times 5=15$

$\therefore$ Sum of observations $=70+15$

$=85$

Mean of the combined set $=\frac{85}{10}=8.5$