8 grams of salt are added to 100 grams of 15% salt water. To make the concentration of the solution 20%, how many grams of water must be added.
100克15%浓度的盐水中，放进了盐8克，为使溶液的浓度为20%，那么，还得再加进水多少克．
<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>