【Question 2】Using 1 one, 2 twos, 2 threes to form some four-digit numbers, the total number of different four-digit numbers that can be formed is $\qquad$.

Translating the above text into English, please retain the original text's line breaks and format, and output the translation result directly.
Analysis: First, selecting 4 numbers from 5 numbers results in three cases:
(1): 1, 2, 2, 3 can form $\frac{A_{4}^{4}}{A_{2}^{2}}=12$ different four-digit numbers
(2): 1, 2, 3, 3 can form $\frac{A_{4}^{4}}{A_{2}^{2}}=12$ different four-digit numbers
(3): 2, 2, 3, 3 can form $\frac{A_{4}^{4}}{A_{2}^{2} \times A_{2}^{2}}=6$ different four-digit numbers

In total, $12+12+6=30$ different four-digit numbers can be formed.