If 100 grams of brine with a concentration of 20% and 200 grams of brine with a concentration of 12.5% are mixed, what is the concentration of the brine obtained after mixing?
现有浓度为20%的盐水100克和浓度为12.5%的盐水200克，混合后所得的盐水的浓度为多少？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">100 * (1/5)</gadget>
<output>20</output>

<gadget id="calculator">12.5 / 100</gadget>
<output>0.125</output>

<gadget id="calculator">200 * 0.125</gadget>
<output>25</output>

<gadget id="calculator">20 + 25</gadget>
<output>45</output>

<gadget id="calculator">100 + 200</gadget>
<output>300</output>

<gadget id="calculator">45 / 300</gadget>
<output>3/20 = around 0.15</output>

<result>3/20 = around 0.15</result>