12. (6 points) From 5 cards labeled with $1,2,3,4,5$, any 3 cards are drawn to form a three-digit number. Among these, the numbers that cannot be divided by 3 are $\qquad$ in total.
【Solution】Solution: $1+2+3=6, 1+2+4=7, 1+2+5=8, 1+3+4=8, 1+3+5=9, 1+4+5=10, 2+3+4$
$$
=9, 2+3+5=10, 2+4+5=11, 3+4+5=12 \text {, }
$$

Among these, the numbers that cannot be divided by 3 are $7, 8, 10, 11$,
Therefore, the three-digit numbers formed by the digits $1, 2, 4; 1, 2, 5; 2, 3, 5$ are not multiples of 3,
That is, the numbers that cannot be divided by 3 are:
$$
\begin{array}{l}
124,142,214,241,412,421 ; \\
125,152,215,251,512,521 ; \\
134,143,314,341,413,431 ; \\
145,154,415,451,514,541 ; \\
235,253,325,352,523,532 ; \\
245,254,425,452,524,542 ;
\end{array}
$$

There are 36 in total.
Therefore, the answer is: 36.