Methodology

Because survey respondents are not asked there exact age, but rather are asked to choose from a set of age "ranges", the best approximation that can be provided for the Avg Age of the respondents is a Weighted Average of the number of respondents X the avg. age of each age range. Consider the following example:

These values are what are retrieved from the U.S Census 2010 SF1 Survey:

From this data, a weighted average calculation is performed as follows: