We have a deck of 52 cards.
We have to calculate the probability that when a card is randomly drawn from the deck, this cart is a red four.
There is only one red four in the deck. Then, if we calculate the probability of an event as the quotient between the number success events (getting a red four, in this case) and the total possible events (getting any card), we will get:
As there is only one card in the deck that gives a success event within the 52 cards, the probability is 1 in 52.
Answer: the probability is 1/52.