There is 300 kg of 10% salt water in container A, and 120 kg of 20% salt water in container B. Now pour the same amount of water into both containers A and B so that the concentration of salt water in the two containers is the same. How many kilograms of water should be poured in?
甲容器中有浓度10%的盐水300千克，乙容器中有20%的盐水120千克，现往甲、乙两容器中倒入等量的水，使这两个容器中盐水的浓度一样，问要倒入多少千克水？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">120 * (1/5) * 300</gadget>
<output>7_200</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">300 * (1/10) * 120</gadget>
<output>3_600</output>

<gadget id="calculator">7_200 - 3_600</gadget>
<output>3_600</output>

<gadget id="calculator">300 * (1/10)</gadget>
<output>30</output>

<gadget id="calculator">120 * (1/5)</gadget>
<output>24</output>

<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<gadget id="calculator">3_600 / 6</gadget>
<output>600</output>

<result>600</result>