8. (5 points) Choose any 3 numbers from $1, 2, 3, 4, 5$ to form a three-digit number, where the number of three-digit numbers that cannot be divided by 3 is $\qquad$.
8. (5 points) From $1, 2, 3, 4, 5$, choose any 3 to form a three-digit number, among which the numbers that cannot be divided by 3 are
18
.

【Solution】Solution: $1+2+3=6, 1+2+4=7, 1+2+5=8, 2+3+4=9, 2+3+5=10, 3+4+5=12$, among these, the sums that cannot be divided by 3 are $7, 8, 10$, i.e., there are three groups $(1, 2, 4), (1, 2, 5), (2, 3, 5)$. Each group can form $3 \times 2 \times 1=6$ numbers, and the three groups can form a total of $6 \times 3=18$ numbers, i.e., there are 18 numbers that cannot be divided by 3.

Therefore, the answer is: 18.