A, B, C, and D donate 60 books in total, the number of books donated by A is (1/2) of the other three people, the number of books donated by B is (1/3) of the other three people, and the number of books donated by C is How many books did Ding donate for the other three (1/4)?
甲、乙、丙、丁四人共捐书60本，甲捐的本数是其余三人的(1/2)，乙捐的本数是其余三人的(1/3)，丙捐的本数是其余三人的(1/4)，丁捐了多少本？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

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

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

<gadget id="calculator">(1/3) + (1/4) + (1/5)</gadget>
<output>47/60 = around 0.783333</output>

<gadget id="calculator">60 * (47/60)</gadget>
<output>47</output>

<gadget id="calculator">60 - 47</gadget>
<output>13</output>

<result>13</result>