Mary and John have a contract for property and the consideration is that Mary will provide nursing care for the remainder of John's life in exchange for the deed to John's property. Is the consideration valid?

The consideration is valid

Explanation:

A consideration is invalid if it is not agreed to by all the parties involved or if the promises made by both parties are disproportionate in value.

Since Mary and John both signed this contract and they both agreed to the terms that are involved, this consideration is valid. Moreover the terms of the consideration do not seem overwhelming to either Mary or John.

Therefore, anyone of them that does not fulfill his / her part of the consideration has breached the agreement and is punishable by law.