The number of books borrowed by Guangming Primary School is 4 less than the total number (3/20), and 68 new books are purchased. At this time, the number of books is less than the total number of original books (1/20), how many original books are there?
光明小学借出的书比总数的(3/20)少4本，又购进68本新书，这时图书比原有图书总数少(1/20)，求原有图书多少本？
<gadget id="calculator">4 + 68</gadget>
<output>72</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 - (1/20)</gadget>
<output>19/20 = around 0.95</output>

<gadget id="calculator">3 / 20</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 - (3/20)</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">(19/20) - (17/20)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">72 / (1/10)</gadget>
<output>720</output>

<result>720</result>