How many kilograms of water are added to 30 kilograms of salt to obtain salt water with a salt content of 30%.
往30千克盐中加入多少千克水，可得到含盐率为30%的盐水．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">30 / (3/10)</gadget>
<output>100</output>

<gadget id="calculator">100 - 30</gadget>
<output>70</output>

<result>70</result>