If you add 50 grams of 0.7% saline to dilute it with 0.07% normal saline, how many grams of water do you need to add?
现有浓度为0.7%的盐水50克，要把它加水稀释成浓度为0.07%的生理盐水，需要加水多少克？
<gadget id="calculator">0.7 / 100</gadget>
<output>0.007</output>

<gadget id="calculator">0.007 * 50</gadget>
<output>0.35</output>

<gadget id="calculator">0.07 / 100</gadget>
<output>0.0007</output>

<gadget id="calculator">0.35 / 0.0007</gadget>
<output>500</output>

<gadget id="calculator">500 - 50</gadget>
<output>450</output>

<result>450</result>