Randomly draw a number from 20 numbers from 1 to 20, what is the probability that the drawn number is a prime number?
从1～20这20个数中任意抽取一个数，抽到的数为素数的可能性的大小为多少．
<gadget id="calculator">8 / 20</gadget>
<output>2/5 = around 0.4</output>

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