John Grisham's statistical flub

I'm going through a John Grisham phase, having recently finished "The Last Juror" and "The Racketeer". I'm now reading his first work, "A Time to Kill", and like with all his books I just can't put it down once I start. His legal research, not surprisingly, is impeccable. However he appears to have made a mathematical error in Chapter 28 :

           "I hope you do the right thing, Joe Frank. I just hope
            they put you in that jury box. We need some people
            with some sense."

           "Wonder why they picked me?"

           "I heard they fixed up a hundred and fifty summonses.
            They're expectin' about a hundred to show up."

           "What're my chances of gettin' picked?"

           "One in a hundred," said Lela.

           "I feel better then. I really ain't got time to serve,
            what with my farmin' and all."


 There remains the small chance that it was intentional and meant to highlight Lela's lack of numeracy, but I doubt it.