The ratio of the number of male to female students in a certain class was 4:5. After 2 boys were transferred this year, the ratio of male to female students was 13:15. How many students were there in this class?
某班原来男女学生的人数的比是4：5，今年又转来2名男生后，男女学生人数的比是13：15，这个班原来有多少人？
<gadget id="calculator">13 / 15</gadget>
<output>13/15 = around 0.866667</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(13/15) - (4/5)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">2 / (1/15)</gadget>
<output>30</output>

<gadget id="calculator">1 + (4/5)</gadget>
<output>9/5 = around 1.8</output>

<gadget id="calculator">30 * (9/5)</gadget>
<output>54</output>

<result>54</result>