There are 30 coins with denominations of 1 yuan and 5 jiao, totaling 24 yuan, how many 1 yuan coins are there?
有面值是1元和5角的硬币共30枚，合计24元，则1元的有多少枚．
<gadget id="calculator">0.5 * 30</gadget>
<output>15</output>

<gadget id="calculator">24 - 15</gadget>
<output>9</output>

<gadget id="calculator">1 - 0.5</gadget>
<output>0.5</output>

<gadget id="calculator">9 / 0.5</gadget>
<output>18</output>

<result>18</result>