The supermarket transfers a batch of beverages. After increasing the profit by 30%, the price of each bottle is 13 yuan. How much is the purchase price? (Solution by equation).
超市调来一批饮料，每瓶增加30%的利润后，售价13元，进价是多少元？(用方程解)．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 + (3/10)</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">13 / (13/10)</gadget>
<output>10</output>

<result>10</result>