bucket of salt water weighs 200 grams, and the ratio of salt to water is 1:19. Now to dilute the bucket of salt water so that the ratio of salt to water is 1:31, how many grams of water should be added?
一桶盐水重200克，其中盐与水的比是1：19，现在要把这桶盐水冲淡，使得盐与水的比为1：31，需加水多少克？
<gadget id="calculator">1 + 19</gadget>
<output>20</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 + 31</gadget>
<output>32</output>

<gadget id="calculator">1 / 32</gadget>
<output>1/32 = around 0.03125</output>

<gadget id="calculator">(1/20) / (1/32)</gadget>
<output>8/5 = around 1.6</output>

<gadget id="calculator">200 * (8/5)</gadget>
<output>320</output>

<gadget id="calculator">320 - 200</gadget>
<output>120</output>

<result>120</result>