It takes 10 hours for a ship to travel downstream from point A to point B, and it takes 15 hours to go upstream from point B to point A. The velocity of the water is 10 kilometers per hour. So how many miles is the flight distance between A and B?
一艘轮船从A地出发去B地为顺流，需10小时；从B地返回A地为逆流，需15小时．水流速度为每小时10千米．那么A、B两地间的航程有多少千米．
<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>1/30 = around 0.033333</output>

<gadget id="calculator">2 / (1/30)</gadget>
<output>60</output>

<gadget id="calculator">10 * 60</gadget>
<output>600</output>

<result>600</result>