The interquartile range is another measure of spread, except that it has the added advantage of not being affected by large outlying values. In order to calculate this value we must first understand ...

There are 31 children in the class. The lower quartile is the \((31+1)\div 4\) value which is the \(8^{th}\) value, which is \(1\). The upper quartile is the \((31+1)\div 4\,\times 3=24^{th}\) value, ...