The inequality is calculated by using mean wealth divide with median wealth. If you learn math before, you should know what is mean and median and hence inequality can be calculated from those two values.
That is one way to calculate the skew in distribution, but is it an appropriate way to measure income inequality? You could have a bell curve, with mean = median and lots of income inequality.
The more accepted means of inequality is the Ginni Coefficient.
http://www.investopedia.com/terms/g/gini-index.asp