There are 20 cards ranging from 1 to 20 in the envelope, draw one at random, how many prime numbers are likely to be drawn.
信封里放着1～20的20张卡片，任意抽一张，抽到质数的可能多少．
<gadget id="calculator">8 / 20</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>