Use a rope to measure the depth of the well, first hang down its (2/3), and then hang down the rest (7/10), which is just right to the end. At this time, there is still 0.5 meters outside the well. How deep is the well in meters?
用绳子测井深，先垂下它的(2/3)，再垂下剩余的(7/10)，才刚好到底，这时井外还余0.5米．井深是多少米？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(1/3) * (3/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">0.5 / (1/10)</gadget>
<output>5</output>

<gadget id="calculator">5 - 0.5</gadget>
<output>4.5</output>

<result>4.5</result>