There are 500 grams of salt water with a water content of 80%. After adding several kilograms of salt, the salt content is 25%. How many kilograms of salt are added to the salt water?
有盐水500克，含水80%加入若干千克盐后，含盐率为25%，在盐水中加入了多少千克的盐？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) * 500</gadget>
<output>125</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">500 * (1/5)</gadget>
<output>100</output>

<gadget id="calculator">125 - 100</gadget>
<output>25</output>

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

<gadget id="calculator">25 / (3/4)</gadget>
<output>100/3 = around 33.333333</output>

<result>100/3 = around 33.333333</result>