A container contains salt water. The teacher asked Xiaoqiang to pour in 800 grams of 5% salt water to make 20% salt water. But Xiaoqiang poured 800 grams of water by mistake. After the teacher found out, he said, it doesn't matter, you can pour 400 grams of the third brine into the container to get 20% brine. What is the concentration of the third brine?
某容器中装有盐水．老师让小强再倒入5%的盐水800克，以配成20%的盐水．但小强却错误地倒入了800克水．老师发现后说，不要紧，你再将第三种盐水400克倒入容器，就可得到20%的盐水了．那么第三种盐水的浓度是多少．
<gadget id="calculator">800 * 0.05</gadget>
<output>40</output>

<gadget id="calculator">400 * 0.2</gadget>
<output>80</output>

<gadget id="calculator">40 + 80</gadget>
<output>120</output>

<gadget id="calculator">120 / 400</gadget>
<output>3/10 = around 0.3</output>

<result>3/10 = around 0.3</result>