5 In the number array shown in the figure, the three numbers in each row form an arithmetic sequence, and the three numbers in each column also form an arithmetic sequences. If $a_{22}=2$, then the sum of all these 9 numbers is $\qquad$
(5) 18 Hint: Method 1 From the given conditions, we have $a_{11}+a_{13}=2 a_{12}, a_{21}+a_{23}=$ $2 a_{22}, a_{31}+a_{33}=2 a_{32}, a_{12}+a_{32}=2 a_{22}$.
Thus, the sum of all 9 numbers is $9 a_{22}=18$.
Method 2 Let all 9 numbers be 2, which clearly satisfies the conditions. Therefore, the sum of all 9 numbers is $9 \times 2=18$.