A number of students stand in a square matrix of 20 rows and 20 columns. If 5 rows and 5 columns are removed, how many people will be reduced?
若干名学生站成一个20行20列的方阵，现去掉其中的5行5列，则减少了多少人．
<gadget id="calculator">20 * 5</gadget>
<output>100</output>

<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">15 * 5</gadget>
<output>75</output>

<gadget id="calculator">100 + 75</gadget>
<output>175</output>

<result>175</result>