5. Let $A, B, C, D$ represent four numbers which are $12, 14, 16, 18$, respectively. Substitute these four numbers into the equation $\mathbf{A} \times \mathbf{B} + \mathbf{B} \times \mathbf{C} + \mathbf{B} \times \mathbf{D} + \mathbf{C} \times \mathbf{D}$, and the maximum value is $\qquad$
【Answer】980
【Analysis】Key point: Maximum value
$$
A \times B+B \times C+B \times D+C \times D=B \times(A+C+D)+C \times D \text {, }
$$

Obviously, $C \times D$ is maximized at $16 \times 18=288$. Next, consider the maximum $B \times(A+C+D)$. Since $B+(A+C+D)=12+14+16+18=60$, the sum is a fixed value. When the sum is fixed, the product of two numbers is maximized when their difference is the smallest. Therefore, the product is maximized when $B$ is 18, which is $18 \times(12+14+16)=756$. However, since there is only one 18, it can only be chosen from $B, C, D$. If $B$ is 18, then the original expression sum is $18 \times(12+14+16)+14 \times 16=980$. If $B$ is 16, then the original expression sum is $16 \times(12+14+18)+14 \times 18=956$. If $B$ is 14, then the original expression sum is $14 \times(12+16+18)+16 \times 18=932$. In summary, the maximum sum of the original expression is 980.