Final answer:
Tony is only obligated to pay the original rent of $400 a month, as the handshake deal with Lydia for a rent increase lacks enforceable consideration, meaning the original lease's terms remain in effect.
Step-by-step explanation:
A student asked about the legal obligations of a tenant, Tony, who agreed to a rental increase but then changed his mind. Tony is only obligated to pay $400 a month because the original lease is a binding contract that cannot be altered without new consideration to support the change.
In this case, a modification to a lease agreement would require additional consideration which is not present just by increasing the rent. Lydia had a reason to raise the rent, but that does not constitute valid consideration. Tony's agreement to pay more was not supported by new consideration from Lydia; therefore, the modification is not enforceable, and the original terms stand.
Tony is obligated to pay $450 a month because the parties have modified the contract in good faith. In this case, Lydia and Tony entered into a new agreement to change the rent amount, and both parties agreed to the new terms. This modification constitutes a valid contract and Tony is legally bound to pay the new rent amount of $450 per month.