There are 12 coins of 1 yuan and 50 cents in the box, totaling 8 yuan and 50 cents. How many coins are there in the box?
盒中装有1元和5角硬币共12枚，共8元5角，其中5角硬币有多少枚．
<gadget id="calculator">12 * 1</gadget>
<output>12</output>

<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">8 + (1/2)</gadget>
<output>17/2 = around 8.5</output>

<gadget id="calculator">12 - (17/2)</gadget>
<output>7/2 = around 3.5</output>

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

<gadget id="calculator">(7/2) / 0.5</gadget>
<output>7</output>

<result>7</result>