It takes a sprinter 10 seconds to run 90 meters with the wind, and 10 seconds to run 70 meters with the same wind speed. If there is no wind, how many seconds does it take for the runner to run 100 meters?
一位短跑选手，顺风跑90米用了10秒，在同样风速的情况下，逆风跑70米也用了10秒．如果在无风的情况下，那么这位选手跑100米用多少秒．
<gadget id="calculator">90 / 10</gadget>
<output>9</output>

<gadget id="calculator">70 / 10</gadget>
<output>7</output>

<gadget id="calculator">9 + 7</gadget>
<output>16</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">16 * (1/2)</gadget>
<output>8</output>

<gadget id="calculator">100 / 8</gadget>
<output>25/2 = around 12.5</output>

<result>25/2 = around 12.5</result>