Two containers, A and B, are respectively filled with 400 liters of water and 50% alcohol. For the first time, half of the alcohol solution is poured from B to A, after mixing, half is poured from A to B, and after mixing, it is poured from B. Give half of the middle to A. How many liters of pure alcohol is contained in A at this time?
甲、乙两个容器分别装有水及浓度为50%的酒精各400升，第一次从乙中倒给甲一半酒精溶液，混合后再从甲中倒一半给乙，混合后再从乙中倒一半给甲．此时甲中含有多少升纯酒精？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 2 / 2</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">400 * (1/8)</gadget>
<output>50</output>

<gadget id="calculator">(1/2) / 2</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">400 * (1/4)</gadget>
<output>100</output>

<gadget id="calculator">100 + 50</gadget>
<output>150</output>

<gadget id="calculator">150 / 2</gadget>
<output>75</output>

<gadget id="calculator">50 + 75</gadget>
<output>125</output>

<result>125</result>