请问平均数为什么不是10个数平均

问题如下：

For Year 6-Year 10, the mean absolute deviation of the MSCI World Index total returns is closest to:

选项：

解释：

A is correct. The formula for mean absolute deviation (MAD) is:

$MDA = \frac{{\sum\limits_{i = 1}^n {\left| {{X_i} - \bar X} \right|} }}{n}$

Column 1: Sum annual returns and divide by n to find the arithmetic mean (${\bar X}$) of 16.40%.

Column 2: Calculate the absolute value of the difference between each year's return and the mean from Column 1. Sum the results and divide by n to find the MAD.

These calculations are shown in the following exhibit: