There are 40 students in the art group of the school, the number of music group is (2/5) the number of art group, and the number of mathematics group is (4/5). How many people are there in the math group?
学校美术组有40人，音乐组人数是美术组人数的(2/5)，又是数学组人数的(4/5)．数学组有多少人？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(2/5) / (4/5)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">40 * (1/2)</gadget>
<output>20</output>

<result>20</result>