How many kilograms of water need to be evaporated to evaporate 30 kg of salt water containing 15% salt into salt crystal particles containing 90% salt?
将含盐15%的盐水30千克，蒸发成含盐90%的食盐晶体颗粒，需蒸发掉多少千克水？
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(3/20) / (9/10)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">30 * (1/6)</gadget>
<output>5</output>

<gadget id="calculator">30 - 5</gadget>
<output>25</output>

<result>25</result>