数学题：乐乐一家去昆明旅游。他们开车从家里出发，计划12个小时到达，结果前3小时行驶了全程的30%（百分之三十），照这样行驶能提前几小时到昆明？

数学题解答：

12 – 3 ÷ 30% = 2（小时）

其中3 ÷ 30%算出的是照前3小时行驶速度而行完全程的时间。

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