The two masters and apprentices process a batch of machine parts, the master does it alone for 6 hours, and the apprentice does it for 9 hours alone. What percentage of this batch of parts is completed per hour when the master and apprentice work together?
师徒二人加工一批机器零件，师傅单独做6小时完成，徒弟单独做9小时完成．师徒二人合做，每小时完成这批零件的几分之几？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/6) + (1/9)</gadget>
<output>5/18 = around 0.277778</output>

<result>5/18 = around 0.277778</result>