A total of 30 people from the "Environmental Guardian" team of Hope Primary School participated in the tree planting activity. The male students planted 2 trees each, and the female students planted 1 tree in total. The team planted 30 trees in total. So how many male students are there?
希望小学"环保卫士"小分队共30人参加植树活动，男同学每人栽2棵树，女同学两人共栽1棵树，小分队一共栽了30棵树．那么男同学有多少人．
<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<gadget id="calculator">60 - 30</gadget>
<output>30</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 - (1/2)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">30 / (3/2)</gadget>
<output>20</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<result>10</result>