There is a batch of biscuits on the shelf of the supermarket. After 25 packs are sold, the salesperson adds another 12 packs. At this time, the number of packs of biscuits on the shelf is exactly 80% of the original. How many packages of biscuits are there on the shelf?
超市货架上有一批饼干，卖出25包后，营业员又加进了12包，这时货架上饼干的包数恰好是原来的80%．货架上原有饼干多少包？
<gadget id="calculator">25 - 12</gadget>
<output>13</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">13 / (1/5)</gadget>
<output>65</output>

<result>65</result>