15. The answer is $(\mathbf{B})$.

Each of the forty cards, at each draw, has the same probability as any other of being drawn from the deck, and this probability is $1 / 40$. In particular, at the second draw, the card that was drawn the first time, having been put back into the deck, has the same probability of being drawn that it had at the first draw, that is, $1 / 40$.

[Problem proposed by P. Negrini.]
15) From a deck of 40 cards, one is drawn and immediately returned to the deck; the deck is then shuffled, and a new card is drawn. What is the probability that the new card is the same card drawn previously?
(A) $1 / 1600$
(B) $1 / 40$
(C) $1 / 80$
(D) $1 / 20$
(E) $\frac{1}{40 \cdot 39}$