A chemical fertilizer factory produces a batch of chemical fertilizers, and it is planned to complete it in 14 days. Due to the improvement of the operation method, the task is completed 4 days ahead of schedule. How much is the work efficiency increased?
某化肥厂生产一批化肥，计划用14天完成，由于改进了操作方法，提前4天完成了任务，求工作效率提高了百分之几？
<gadget id="calculator">14 - 4</gadget>
<output>10</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 14</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">(1/10) - (1/14)</gadget>
<output>1/35 = around 0.028571</output>

<gadget id="calculator">(1/35) / (1/14)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>