In summary, the "whole" can be split up differently and different parts are greater than or less than other parts.
[tex]\frac{1}{10}[/tex] is smaller than [tex]\frac{1}{5}[/tex], so it will take more [tex]\frac{1}{10}[/tex]s to equal a [tex]\frac{1}{5}[/tex].
-> The exact value is two [tex]\frac{1}{10}[/tex]s per [tex]\frac{1}{5}[/tex]
4 copies of 1 tenth = [tex]\frac{4}{10}[/tex]
2 copies of 1 fifth = [tex]\frac{2}{5}[/tex]
They are both equal to [tex]\frac{2}{5}[/tex], but [tex]\frac{4}{10}[/tex] is broken up into smaller pieces. This is why it takes more tenths to equal a fifth.
[tex]\frac{4}{10}[/tex] = [tex]\frac{4/2}{10/2} =\frac{2}{5}[/tex] which is equal to [tex]\frac{2}{5}[/tex].