The salt content of seawater is 5%. How many kilograms of fresh water should be added to 40 kg of seawater to make the salt content of seawater 2%.
海水中盐的含量为5%，在40千克海水中，需加入多少千克淡水才能使海水中盐的含量为2%．
<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">2 / 100</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/20) / (1/50)</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">40 * (5/2)</gadget>
<output>100</output>

<gadget id="calculator">100 - 40</gadget>
<output>60</output>

<result>60</result>