The completion time of building a building is reduced from 120 days to 90 days. How much is the time ahead? How many columns are correct?
盖一座大楼完成时间由120天减少到90天，时间提前百分之几？正确的列式有多少．
<gadget id="calculator">120 - 90</gadget>
<output>30</output>

<gadget id="calculator">30 / 120</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>