The number of students in Class 1 of the sixth grade is between 50 and 60. The ratio of the number of boys to the number of girls in this class is 4:5. How many girls are there in this class?
六年级一班的学生人数在50到60之间，这个班的男生人数和女生人数的比是4：5，这个班有女生多少人．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

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

<result>30</result>