Qingqing Fruit Shop bought a batch of watermelons and planned to sell them at a price of 15% profit, but they didn't sell any of them, so they had to sell all the watermelons at 20% off the price, resulting in a loss of 10 yuan. How much is the purchase price of this batch of watermelons?
青青果品店进了一批西瓜，打算以15%的利润为定价卖出，谁知一个都没卖出，只能以定价的八折将这批西瓜全部卖完，结果亏了10元．这批西瓜进价是多少元？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/20) * (4/5)</gadget>
<output>3/25 = around 0.12</output>

<gadget id="calculator">1 - (4/5) - (3/25)</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">10 / (2/25)</gadget>
<output>125</output>

<result>125</result>