It takes 10 hours for a car to go from A to B, and after driving for 3 hours, it stops at a distance of 50 kilometers from the midpoint. How many kilometers are there between A and B?
汽车从甲地到乙地要10小时，行了3小时后，在距离中点50千米处暂停．甲、乙两地相距多少千米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/2) - (3/10)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">50 / (1/5)</gadget>
<output>250</output>

<result>250</result>