Hope Primary School has 720 students, and the ratio of girls to boys is 4:5. How many boys are there in this school?
希望小学有学生720人，女生人数与男生人数的比是4：5，这所学校有男生多少人？
<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">720 * (5/9)</gadget>
<output>400</output>

<result>400</result>