If the ratio of the number of girls to boys in a class is 4:5, what is the number of girls in the class?
某班的女生人数与男生人数比是4：5，那么女生人数是这班人数的多少．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<result>4/9 = around 0.444444</result>