A bottle of salt water, the mass ratio of salt to water is 1:20, if you add 50 grams of water, it will become salt water with a salt content of 4%. How many grams of salt water is in the original bottle?
一瓶盐水，盐与水的质量比是1：20，如果再放入50克水，就变成含盐率是4%的盐水．原来瓶内盐水有多少克？
<gadget id="calculator">4 / 100</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">50 * (1/25)</gadget>
<output>2</output>

<gadget id="calculator">50 * (1/25) * 20</gadget>
<output>40</output>

<gadget id="calculator">2 + 40</gadget>
<output>42</output>

<gadget id="calculator">(1/25) * 20</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (1/25) - (4/5)</gadget>
<output>4/25 = around 0.16</output>

<gadget id="calculator">42 / (4/25)</gadget>
<output>525/2 = around 262.5</output>

<result>525/2 = around 262.5</result>