Four students planted 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. The third student planted The tree is 1/4 of the total number of trees planted by other students. The fourth student just planted 13 trees. Ask the first student how much of the total number of trees planted? Why?
四位同学去植树，第一位同学植的树是其他同学植树总数的(1/2)，第二位同学植的树是其他同学植树总数的(1/3)，第三位同学植的树是其他同学植树总数的(1/4)，第四位同学刚好植了13棵，问第一位同学植的棵数占总数的多少？为什么？
<gadget id="calculator">1 + 2</gadget>
<output>3</output>

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

<result>1/3 = around 0.333333</result>