The ratio of the number of sixth graders participating in physical exercise to the total number of grades is 1:4. If the 18 students who participate in chess activities are counted, it will account for (1/3) of the total number of students in the whole grade. How many students are there in grade six?
六年级参加体育锻炼的人数与年级总人数的比是1：4，如果算上棋类活动的18人，就占到全年级总人数的(1/3)．六年级有学生多少人？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/3) - (1/4)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">18 / (1/12)</gadget>
<output>216</output>

<result>216</result>