Put 8 grams of salt into 100 grams of 15% brine, how many grams of water should be added to make the concentration 20%.
100克浓度为15%的盐水中，放进8克盐，若要使其浓度变成20%，还要再加多少克水．
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">100 * (3/20)</gadget>
<output>15</output>

<gadget id="calculator">15 + 8</gadget>
<output>23</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">23 / (1/5)</gadget>
<output>115</output>

<gadget id="calculator">100 + 8</gadget>
<output>108</output>

<gadget id="calculator">115 - 108</gadget>
<output>7</output>

<result>7</result>