Question

If $150$ is the mean of $200$ observations and $100$ is the mean of some $300$ other observations, find the mean of the combination.

• A. $90$
• B. $100$
• C. $120$
• D. $150$

Answer 1

The correct option is C $120$

Mean of $200$ observations = $150$
Sum of $200$ observations = $200\times 150=30000$
Mean of $300$ observations = $100$
Sum of $300$ observations = $300\times 100=30000$
Total Sum = $30000+30000=60000$
Number of observations = $100+200=500$
Mean = $\frac{Sum}{Numberofobservations}=\frac{60000}{500}=120$