Well I worked out that this formula results in the answer at the end of the book.

I'm still trying to understand why, but I think it's becuase there are 52 single cards in the deck, just like if I was to roll two dice and get a 9, there are four ways out of the thirty-six simple events that can result in a 9. So I'm thinking that you have to multiply it by 52 because there are 52 different simple events that could be the single card chosen by the first person.

regards.