a. Holden was desperate for companionship and thought Luce was intellectual and could help him.
b. He wanted to borrow money. He knew Luce was rich, and was a sucker for a sob story.
c. Luce has his own apartment, and Holden figured Luce would let him stay with him until Wednesday.
d. Holden knew Luce was an A student and wanted tuotoring.