Take 500 grams of salt water with a salt content of 10%, and heat it with fire to partially evaporate the water in it. When the salt content of the salt water becomes 50%, how many grams of water has evaporated?
有含盐率10%的盐水500克，用火加热，使其中的水分部分蒸发，当盐水的含盐率变为50%时，已经蒸发水分多少克．
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">500 * (1/10)</gadget>
<output>50</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">50 / (1/2)</gadget>
<output>100</output>

<gadget id="calculator">500 - 100</gadget>
<output>400</output>

<result>400</result>