The school organized a martial arts performance. First, 25 boys and 20 girls were selected to participate. Later, 12 girls were added. To keep the ratio of the number of boys and girls unchanged, how many boys should be added?
学校组织武术操表演，先挑选了男生25人，女生20人参加，后来又增加了女生12人，要使男女生人数的比值不变，男生应增加多少人人．
<gadget id="calculator">20 + 12</gadget>
<output>32</output>

<gadget id="calculator">32 / 4</gadget>
<output>8</output>

<gadget id="calculator">5 * 8</gadget>
<output>40</output>

<gadget id="calculator">40 - 25</gadget>
<output>15</output>

<result>15</result>