Two trains depart from AB at the same time. If the journey is complete, the express train will take 10 hours and the slow train will take 15 hours. After 2 hours, the distance between the two trains will be 600 kilometers. Find the distance between AB and AB.
两列火车分别从AB两地同时相对开出，如行完全程，快车要10小时，慢车要15小时，两车开出2小时后，还相距600千米，求AB两地距离．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/10) + (1/15)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) * 2</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">600 / (2/3)</gadget>
<output>900</output>

<result>900</result>