There are 45 students in Class 1 of Hope Primary School. It is known that the ratio of boys to girls in this class is 5:4. How many girls are there in this class?
希望小学六一班有45人，已知这个班男、女生人数的比是5：4，这个班女生有多少人．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">45 / 9</gadget>
<output>5</output>

<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<result>20</result>