There are 160 books in three categories. If A (1/3), B (1/4), and C (1/5) are borrowed for the first time, there are still 120 books left. If A is borrowed for the first time ( 1/5), B's (1/4), C's (1/3), there are 116 books left, ask the original B's books how many books.
三类读物160本，如果第一次借出A的(1/3)，B的(1/4)，C的(1/5)，还剩120本，若第一次借出A的(1/5)，B的(1/4)，C的(1/3)，还剩116本，问原B读物多少本．
<gadget id="calculator">168 - 160</gadget>
<output>8</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">8 / (1/15)</gadget>
<output>120</output>

<gadget id="calculator">160 - 120</gadget>
<output>40</output>

<result>40</result>