Add 10 kilograms of water to a bucket filled with water, and then take out 70% of it. At this time, the water in the bucket is equal to (2/5) of the original water. How many kilograms of water are there in the original bucket?
在一盛水的桶里在加进10千克水，然后取出70%，这时桶里的水等于原来水的(2/5)，原来桶里有水多少千克？
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">10 * (7/10)</gadget>
<output>7</output>

<gadget id="calculator">10 - 7</gadget>
<output>3</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) - 1</gadget>
<output>-3/5 = around -0.6</output>

<gadget id="calculator">(7/10) + (-3/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">3 / (1/10)</gadget>
<output>30</output>

<result>30</result>