The four students planted a total of 60 trees. The first student planted (1/2) the total number of trees planted by other students, the second student planted (1/3) the total number of trees planted by other students, and the second student planted (1/3) the total number of trees planted by other students. The three students planted 1/4 of the total number of trees planted by other students. How many trees did the fourth student plant?
四位同学共种60棵树，第一位同学种的树是其他同学种树总数的(1/2)，第二位同学种的树是其他同学种树总数的(1/3)，第三位同学种的是其他同学种树总数的(1/4)，第四位同学种了多少棵树？
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

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

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

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

<gadget id="calculator">1 - (1/3) - (1/4) - (1/5)</gadget>
<output>13/60 = around 0.216667</output>

<gadget id="calculator">60 * (13/60)</gadget>
<output>13</output>

<result>13</result>