The ratio of the number of boys and girls in Class 1 of six years is 4:5. It is known that there are 20 boys and how many girls are there.
六年一班男女生人数的比是4：5，已知男生有20人，女生有多少人．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<result>25</result>