Put 10 grams of sugar into 40 grams of water and let it stand for 3 days. After evaporation, the sugar water is only 40 grams. How much is the concentration of sugar water after evaporation? (Adapted from the teaching material test question bank)
把10克糖放入40克水中，放置3天，蒸发后的糖水只有40克，蒸发后糖水的浓度比原来提高了百分之几？(根据教学资料试题库改编)
<gadget id="calculator">10 / 40</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">10 + 40</gadget>
<output>50</output>

<gadget id="calculator">10 / 50</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) / (1/5)</gadget>
<output>1/4 = around 0.25</output>

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