There are 50 kilograms of brine with a salt content of 10%, and its mass fraction should be increased to 20%. How many kilograms of salt need to be added?
现有含盐10%的盐水50千克，要将它的质量分数提高到20%．需要加盐多少千克？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">50 * (9/10)</gadget>
<output>45</output>

<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">45 / (4/5)</gadget>
<output>225/4 = around 56.25</output>

<gadget id="calculator">(225/4) - 50</gadget>
<output>25/4 = around 6.25</output>

<result>25/4 = around 6.25</result>