Answer :
[tex]\overline{x}-arithmetic\ mean\\\\\overline{x}=\frac{20+25+30+30+45}{5}=\frac{150}{5}=30\\\\the\ mean\ absolute\ deviation:\delta=\frac{|x_1-\overline{x}|+|x_2-\overline{x}|+|x_3-\overline{x}|+...+|x_n-\overline{x}|}{n}\\\\\delta=\frac{|20-30|+|25-30|+|30-30|+|30-30|+|45-30|}{5}=\frac{|-10|+|-5|+|0|+|0|+|15|}{5}\\\\=\frac{10+5+0+0+15}{5}=\frac{30}{5}=\boxed{6}\leftarrow answer[/tex]
