The master and the apprentice process a batch of parts together, the master needs 9 hours to process this batch of parts, and the apprentice needs 15 hours to process this batch of parts, so how much slower is the apprentice than the master
师傅和徒弟同加工一批零件，师傅加工这批零件需要9小时，徒弟加工这批零件需要15小时，那么徒弟比师傅慢多少
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

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

<gadget id="calculator">(1/9) - (1/15)</gadget>
<output>2/45 = around 0.044444</output>

<gadget id="calculator">(2/45) / (1/9)</gadget>
<output>2/5 = around 0.4</output>

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