Put a 7-meter-long bamboo pole into the pool, (1/5) is exposed to the water, and the rest (2/7) is inserted into the mud. How deep is the water?
把一根长7米得竹竿插在池里，(1/5)露出水面，其余的(2/7)插在泥里，问水深多少米？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(4/5) * (2/7)</gadget>
<output>8/35 = around 0.228571</output>

<gadget id="calculator">1 - (8/35) - (1/5)</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">7 * (4/7)</gadget>
<output>4</output>

<result>4</result>