In the school group gymnastics performance, there are 400 boys and 340 girls, and 20 people stand in each row. How many rows are girls standing less than boys?
在学校团体操表演中，男生有400人，女生有340人，每行站20人，女生比男生少站多少行．
<gadget id="calculator">400 / 20</gadget>
<output>20</output>

<gadget id="calculator">340 / 20</gadget>
<output>17</output>

<gadget id="calculator">20 - 17</gadget>
<output>3</output>

<result>3</result>