There is 30 kg of salt water with a salt content of 15%. According to the need, to make the salt content of the salt water 25%, how much salt can we add?
有含盐率为15%的盐水30千克，根据需要，要使盐水的含盐率变为25%，那么，我们可以加盐多少千克．
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 - (3/20)</gadget>
<output>17/20 = around 0.85</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">(17/20) / (3/4)</gadget>
<output>17/15 = around 1.133333</output>

<gadget id="calculator">30 * (17/15)</gadget>
<output>34</output>

<gadget id="calculator">34 - 30</gadget>
<output>4</output>

<result>4</result>