There are 40 kilograms of salt water with 15% salt content, what should be done if we want to change this salt water to 20% salt water? (Add 2 points for two different ways of thinking. Prompting different ways of thinking means that the answer is open)
现有含盐15%的盐水40千克，要把这种盐水变为含盐20%，应该怎么办？(用两种不同的思路另加2分．提示不同的思路指答案开放)
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) * 40</gadget>
<output>8</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/20) * 40</gadget>
<output>6</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2 / (4/5)</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>