There used to be 4 billion species of creatures living on the earth, but now there are only about 50 million species of creatures in the world. After a long period of time, how many of them have become extinct.
地球上曾经生活着40亿种生物，而到现在全球只有约5000万种生物，经过漫漫的岁月淘汰，其中多少的生物已经灭绝．
<gadget id="calculator">40 - 0.5</gadget>
<output>39.5</output>

<gadget id="calculator">39.5 / 40</gadget>
<output>0.9875</output>

<result>0.9875</result>