If 150 kg of brine contains 20% salt, how many kg of salt should be added to turn it into brine with a salt content of 25%.
含盐20%的盐水150千克，要变成含盐率为25%的盐水需加盐多少千克．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(4/5) / (3/4)</gadget>
<output>16/15 = around 1.066667</output>

<gadget id="calculator">150 * (16/15)</gadget>
<output>160</output>

<gadget id="calculator">160 - 150</gadget>
<output>10</output>

<result>10</result>