4. (4 points) Use equally long sticks to form triangles in the following manner. Then, to form 12 triangles, you need $\qquad$ sticks.

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4. (4 points) Use equally long sticks to form triangles in the following manner. Then, to form 12 triangles, you need $\qquad$ sticks.
【Answer】Solution: A triangle requires 3 sticks,
2 triangles require $3+2=5$ sticks,
3 triangles require $3+2 \times 2=7$ sticks,
$\qquad$
12 triangles require $3+2 \times(12-1)=25$ sticks.
Answer: It takes 25 sticks to arrange 12 triangles.
Therefore, the answer is: 25.