120 g of 5% brine, 300 g of 7% brine, and 100 g of 12% brine are mixed together. What is the concentration of the resulting mixture?
有浓度为5%的盐水120克，浓度为7%的盐水300克，浓度为12%的盐水100克混合在一起，得到的混合溶液的浓度为多少．
<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">120 * (1/20)</gadget>
<output>6</output>

<gadget id="calculator">7 / 100</gadget>
<output>7/100 = around 0.07</output>

<gadget id="calculator">300 * (7/100)</gadget>
<output>21</output>

<gadget id="calculator">12 / 100</gadget>
<output>3/25 = around 0.12</output>

<gadget id="calculator">(3/25) * 100</gadget>
<output>12</output>

<gadget id="calculator">6 + 21 + 12</gadget>
<output>39</output>

<gadget id="calculator">120 + 300 + 100</gadget>
<output>520</output>

<gadget id="calculator">39 / 520</gadget>
<output>3/40 = around 0.075</output>

<result>3/40 = around 0.075</result>