3. From 5 cards each written with the numbers $1, 2, 3, 4, 5$, any 2 cards are taken out. The number on the first card is used as the tens digit, and the number on the second card is used as the units digit to form a two-digit number. Then the probability that the number formed is a multiple of 3 is ( ).
(A) $\frac{1}{5}$
(B) $\frac{3}{10}$
(C) $\frac{2}{5}$
(D) $\frac{1}{2}$
3. C.

The two-digit numbers that can be formed are
$$
\begin{array}{l}
12,13,14,15,21,23,24,25,31,32, \\
34,35,41,42,43,45,51,52,53,54,
\end{array}
$$

a total of 20. Among these, the numbers that are multiples of 3 are
$$
12,15,21,24,42,45,51,54 \text {, }
$$

a total of 8. Therefore, the probability that a number formed is a multiple of 3 is $\frac{8}{20}=\frac{2}{5}$.