Teacher Zhao went to the bookstore to order the new edition of "Hope Mathematics" in 2005. The book is divided into volumes 1 and 2. With the money Mr. Zhao brings, if he only buys the first volume, he can buy exactly 40 copies, and if he only buys the second volume, he can buy exactly 60 copies. Then how many sets of books can be ordered with the money Mr. Zhao brings (one set for the upper and lower volumes).
赵老师去书店订购《希望数学》2005年新版书，该书分上、下册．赵老师所带的钱如果只买上册恰好可买40本，如果只买下册恰好可买60本．那么赵老师所带的钱可以订购多少套书(上、下册各一本为一套)．
<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/60) + (1/40)</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">1 / (1/24)</gadget>
<output>24</output>

<result>24</result>