It is necessary to evaporate part of the water from 40 kilograms of salt water with a salt content of 12.5% to produce a salt water with a salt content of 20%. Question: How much salt water should be produced in the end?
要从含盐率12.5%的盐水40千克里，蒸发掉一部分水，制成含盐20%的盐水，问：最后应制成多少盐水？
<gadget id="calculator">12.5 / 100</gadget>
<output>0.125</output>

<gadget id="calculator">40 * 0.125</gadget>
<output>5</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">5 / (1/5)</gadget>
<output>25</output>

<result>25</result>