What is the probability of drawing a prime number among twenty cards with numbers 1-20 written on them?
在写有1～20的二十张卡片中，抽到质数的可能性是多少．
<gadget id="calculator">8 / 20</gadget>
<output>2/5 = around 0.4</output>

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