There are 45 teachers and students in the school to participate in voluntary activities in the community, including male students (4/9) and female students (2/9). How many male students participate in voluntary activities?
学校有45名师生到社区参加义务活动，其中男同学占(4/9)，女同学占(2/9)．参加义务活动的男同学有多少人？
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">45 * (4/9)</gadget>
<output>20</output>

<result>20</result>