There is a pile of coal, 3.5 tons have been used, and the ratio of the remaining tons to the tons of coal used is 5:2. How many tons is there in this pile of coal? (3 solutions. Only list, not calculation)
有一堆煤，已经用了3.5吨，剩下的吨数与用去煤的吨数的比是5：2，原来这堆煤有多少吨？(3种解法．只列式，不计算)
<gadget id="calculator">3.5 * 5</gadget>
<output>17.5</output>

<gadget id="calculator">3.5 * 2</gadget>
<output>7</output>

<gadget id="calculator">17.5 + 7</gadget>
<output>24.5</output>

<gadget id="calculator">24.5 / 2</gadget>
<output>12.25</output>

<result>12.25</result>