From point A to point B, car A takes 10 hours to complete the journey, and car B takes 15 hours to complete the journey. Cars A and B are traveling towards each other from A and B at the same time, and meet at a distance of 40 kilometers from the midpoint of A and B. How many kilometers are there between A and B?
从A地到B地，甲车走完全程需10小时，乙车走完全程需15小时．甲乙两车分别从A、B两地同时相向而行，在距A、B两地中点40千米处相遇，求A、B两地相距多少千米？
<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 / (1/6)</gadget>
<output>6</output>

<gadget id="calculator">(1/10) - (1/15)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">6 * (1/30)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">2 / (1/5)</gadget>
<output>10</output>

<gadget id="calculator">40 * 10</gadget>
<output>400</output>

<result>400</result>