The ratio of the number of male to female students in a class was 3:4, and 2 girls were transferred later. At this time, the ratio of male to female students was 5:7. How many girls are there in this class?
某班原有男女生人数的比是3：4，后来又转来2名女生，这时男女人数的比是5：7．这个班现有女生多少人？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">2 / (1/20)</gadget>
<output>40</output>

<gadget id="calculator">7 / 5</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">40 * (7/5)</gadget>
<output>56</output>

<result>56</result>