Bava Metzia 54 - Adding One-Fifth (Finds)

When one redeems the second tithe taken from his produce for money, he must add 1/5. In many other cases, 1/5 is added, such as when redeeming property belonging to the Temple treasury or repaying a Kohen's portion (trumah) that one has accidentally eaten. 

Is the 1/5 calculated on the principal ("from the inside) or on the principal plus the addition ("from the outside")?

For example, adding a 1/5 to 20 can mean paying 4 (1/5 of 20.) It can also mean 5 since the total is 25, and 1/5 is 5.

The answer is that 1/5 is calculated from the outside and is 1/4 of the principal.

Art: Our Village Clockmaker Solving a Problem by James Campbell

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