The water in a pool is used up (2/7), and there are 20 tons left. How many tons of water is there in this pool?
一水池的水用去(2/7)，还剩20吨，这池水本来有多少吨？
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/7)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">20 / (5/7)</gadget>
<output>28</output>

<result>28</result>