Question

Find the mean of first $10$ multiples of $3$.

• A. $15.5$
• B. $17.5$
• C. $16.5$
• D. $18.5$

Answer 1

Answer: (C)

$16.5$

Answer 2

First $10$ multiples of $3$ are $3$, $6$, $9$, $12$, ..., $30$. This is an $A.P.$ with $a = 3$, $n = 10$ and $l = 30$. $\therefore$ sum $= \frac{n}{2}\left(a+l\right)$ $=\frac{10}{2}\cdot\left(3+30\right)=165$ $\therefore$ Mean, $\bar{x} = \frac{165}{10} = 16.5$.