A and B walk from A to B at the same time. When A walks the whole distance (1/4), B is still 640 meters away from B. When A walks the rest (5/6), B walks the whole distance. (7/10), how many meters is the distance between AB and AB?
甲乙两人同时从A地步行走向B地，当甲走了全程的(1/4)时，乙离B地还有640米，当甲走余下的(5/6)时，乙走完全程的(7/10)，求AB两地距离是多少米？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(3/4) * (5/6)</gadget>
<output>5/8 = around 0.625</output>

<gadget id="calculator">(1/4) + (5/8)</gadget>
<output>7/8 = around 0.875</output>

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

<gadget id="calculator">(7/8) / (7/10)</gadget>
<output>5/4 = around 1.25</output>

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

<gadget id="calculator">(1/4) * (4/5)</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">640 / (4/5)</gadget>
<output>800</output>

<result>800</result>