There are 13 fours in a deck of cards (one for each suit), so the probability of picking a 4 is 13/52.
The complement of not picking a 4 is picking any card that is not a 4. There are 52 total cards in the deck, and 13 of them are fours. So, there are 52 - 13 = 39 cards that are not a 4.
Therefore, the probability of not picking a 4 is 39/52.
The complement of not picking a 4 is the probability of picking a 4, so the answer is 13/52, which simplifies to 1/4.