Of the 5 keys only 1 can open the door. If one of them is chosen, what is the probability of opening the door?
5把钥匙只有1把能打开门．任选其中的1把，打开门的可能性是多少．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>