my.cards <- list(c("red", "black"), c("black", "black"), c("red", "red"))

### choose a card at random

draw.card <- function (cards = my.cards)
{
  i <- sample(cards, 1)[[1]]
}

### choose a random orientation for a card

random.flip <- function(card)
{
  i <- sample(1:2, 1)
  if (i == 1)
    c(card[1], card[2])
  else
    c(card[2], card[1])
}

### draw a random card and random side; compute the probability that
### the other side is red.

do.card.trick <- function(n = 10000)
{
  study <- data.frame(t(sapply(1:n,
                               function (i) random.flip(draw.card(my.cards)))))
  my.table <- table(subset(study, X1=="red")[, 2])
  my.table / sum(my.table)
}