Is the additional one fifth payment added when redeeming an item that you designated for the beit hamikdash also added to a secondary hekdesh (something you bought with that coin and then want to redeem that item also)? The mishna lists minimum amount of money for various laws. And 5 laws for which the minimum amount is a pruta. Levi has a different list of what are the five items and the gemara disucsses why they each differ from each other. The mishna lists 5 cases where one needs to add one fifth. One of the items if d’mai – which is a rabbinic obligation (a case where it is doubtful if trumot and maasrot were taken). The gemara questions why the rabbis would insist that one would add a fifth if one ate d’mai – why would it be treated as stringently as a Torah obligation? They answer that it is according to rabbi Meir’s approach that the rabbis do make their decrees as strong as the Torah and it is proven from a case of divorce law where Rabbi Meir is stringent.