Add 5 kg of table salt to a bucket of salt water with a salt content of 10%. After dissolving, the concentration of salt water in the bucket will be 20%. How many kilograms of salt water are there in the bucket?
在一桶含盐量为10%的盐水中加入5千克食盐，溶解后，桶中盐水的浓度为20%，桶中原来有盐水多少千克？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/5) - (1/10) - 1</gadget>
<output>-9/10 = around -0.9</output>

<gadget id="calculator">1 + (-9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">4 / (1/10)</gadget>
<output>40</output>

<result>40</result>