There are 2 cups of the same size, one cup of 30% salt water in A, half a cup of 10% salt water in B, first pour half of the salt water in cup A into cup B, stir well, then pour half of cup B back into cup A , At this time, what is the concentration of a cup of salt water.
有同样大小的杯子2个，甲装30%的盐水一杯，乙装10%的盐水半杯，先将甲杯盐水的一半倒入乙杯中，搅匀后再将乙杯一半倒回甲杯，这时甲杯盐水的浓度是多少．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">15 + 10</gadget>
<output>25</output>

<gadget id="calculator">25 + 75</gadget>
<output>100</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>