Duffer then rejected Slicker's bike on the ground that he had already bought Koolcat's"In a lawsuit by Slicker against Duffer for breach of contract, what would the court probably decide regarding Slicker's letter of October 9?
Mailing of the letter by Slicker did not, of itself, prevent a subsequent, effective revocation by Duffer of his offer. 
The letter bound both parties to a bilateral contract, but only when received by Duffer on November 10. 
Regardless of whether Duffer's offer had proposed a unilateral or a bilateral contract, the letter was an effective acceptance upon receipt, if not upon dispatch
The letter bound both parties to a unilateral contract as soon as Slicker mailed it.