Central Primary School has a total of 720 students, among which the sixth grade is the whole school (1/4), the seventh grade is the whole school (5/24), the eighth grade is the whole school (7/24), how many are the ninth grade?
中心小学共有学生720人，其中六年级是全校人数的(1/4)，七年级是全校人数的(5/24)，八年级是全校人数的(7/24)，九年级有多少人？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">5 / 24</gadget>
<output>5/24 = around 0.208333</output>

<gadget id="calculator">7 / 24</gadget>
<output>7/24 = around 0.291667</output>

<gadget id="calculator">1 - (1/4) - (5/24) - (7/24)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">720 * (1/4)</gadget>
<output>180</output>

<result>180</result>