A pile of chess pieces has two colors of black and white, among which black pieces account for (1/5), if the number increases to 10 white pieces, then black pieces account for (2/7). So, how many pieces are there in this pile.
一堆棋子有黑白两种颜色，其中黑子占(1/5)，若增加到10枚白子，这时黑子占(2/7)．那么，这堆棋子有多少枚．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/7)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">10 / (5/7)</gadget>
<output>14</output>

<result>14</result>