Question:
The arithmetic mean of 1, 2, 3, ... , n is
(a) $\frac{n+1}{2}$
(b) $\frac{n-1}{2}$
(c) $\frac{n}{2}$
(d) $\frac{n}{2}+1$
Solution:
Arithmetic mean of 1, 2, 3, ... , n
$=\frac{1+2+3+\ldots+n}{n}$
$=\frac{\frac{n(n+1)}{2}}{n}$
$=\frac{n+1}{2}$
Hence, the correct option is (a).
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