Master Zhang processes a part. It used to take 15 minutes to process one part, but now it only takes 12 minutes to process one part. How much work efficiency has been improved?
张师傅加工一种零件，原来加工一个需要15分钟，现在加工一个只需要12分钟，工作效率提高多少．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) - (1/15)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/60) / (1/15)</gadget>
<output>1/4 = around 0.25</output>

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