There are 3 pens of the same model on the table, and one of them has no ink. What is the probability that Xiaoli takes one at random but cannot write?
桌上放着3支同样型号的钢笔，其中1支没有墨水，小丽随意拿1支却写不出字的可能性大小是多少．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>