Four students planted trees. The first student planted the trees of the other students (1/2), the second student planted the trees of the other students (1/4), and the third student planted the trees of the other students. (1/5) of the total number of students, and the fourth student just planted 15 trees. How many trees did the four students plant in total?
四位同学去植树，第一位同学植的树是其他同学总数的(1/2)，第二位同学植的树是其他同学的(1/4)，第三位同学植的树是其他同学总数的(1/5)，而第四位同学则刚好植了15棵．问四位同学一共植树多少棵？
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 + 4</gadget>
<output>5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + 5</gadget>
<output>6</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 - (1/3) - (1/5) - (1/6)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">15 / (3/10)</gadget>
<output>50</output>

<result>50</result>