There are 45 students in the second class of the sixth grade, including 21 girls, and how many more girls are added. At this time, the number of girls is exactly (1/2) of the whole class.
六年级二班共有学生45人，其中女生有21人，再增加多少名女生，这时女生人数刚好是全班人数的(1/2)．
<gadget id="calculator">45 - 21</gadget>
<output>24</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">24 / (1/2)</gadget>
<output>48</output>

<gadget id="calculator">48 - 45</gadget>
<output>3</output>

<result>3</result>