The city of Providence, Rhode Island, decided to hire a class of police officers in 2001. All had to graduate from the Providence Police Academy to be eligible. Two sessions were held. To be qualified, the applicants to the academy had to pass a series of tests and be deemed qualified after an interview. Those judged most qualified were sent a letter informing them that they had been selected to attend the academy if they completed a medical checkup and a psychological exam. The letter for the applicants to the 61st Academy, dated October 15, stated that it was a "conditional offer of employment."

1. When the new police chief changed the rules for employment, why was he not permitted to do so legally?
Clue: The reasoning here is similar to the reasoning whenever one party to an agreement decides it does not like the contract it previously formed.
2. What is the relevant rule of law in this case?
Clue: What requirements are imposed once one makes an offer to enter into a unilateral contract?