project was originally planned to be completed in 15 days, but the ratio of the actual number of days to the planned number of days is 4:5. How much has the actual average daily work efficiency improved?
一项工程原计划15天完成，实际所用天数与计划所用天数的比是4：5．实际平均每天的工作效率提高了多少．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">15 * (4/5)</gadget>
<output>12</output>

<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>