Take 500 grams of brine with a concentration of 30% and 100 grams of brine with a concentration of 90%, what is the concentration of the brine after mixing?
取浓度为30%的盐水500克和浓度为90%的盐水100克，混合后的盐水浓度是多少？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">500 * (3/10)</gadget>
<output>150</output>

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

<gadget id="calculator">100 * (9/10)</gadget>
<output>90</output>

<gadget id="calculator">150 + 90</gadget>
<output>240</output>

<gadget id="calculator">500 + 100</gadget>
<output>600</output>

<gadget id="calculator">240 / 600</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">(2/5) * 1</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>