The three classes of the fourth grade participated in the voluntary labor organized by the school. The number of participants in the first and second classes accounted for (13/18) of the total number of fourth graders, and the number of participants in the second and third classes accounted for (11/18) of the total number of fourth graders. What percentage of the number of participants in the second class accounted for the total number of the fourth grade?
四年级三个班参加学校组织的义务劳动，一班和二班参加人数占四年级总人数的(13/18)，二班和三班参加人数占四年级总人数的(11/18)．二班参加人数占四年级总人数的几分之几？
<gadget id="calculator">13 / 18</gadget>
<output>13/18 = around 0.722222</output>

<gadget id="calculator">11 / 18</gadget>
<output>11/18 = around 0.611111</output>

<gadget id="calculator">(11/18) - 1</gadget>
<output>-7/18 = around -0.388889</output>

<gadget id="calculator">(13/18) + (-7/18)</gadget>
<output>1/3 = around 0.333333</output>

<result>1/3 = around 0.333333</result>