The "Treasure Box" interactive link in CCTV's "Lucky 52" column is a guessing game. The rules of the game are as follows: Among the 20 trademarks, there are 5 trademarks with a certain amount of bonus on the back, and the rest of the trademarks on the back. It's a sad face, and if you turn it over, you won't be rewarded. Spectators participating in this game have three chances to flop. A spectator got a certain amount of bonuses in the first two flops. If the turned over cards cannot be flopped again, what is the probability that the spectator will win the third flop
中央电视台"幸运52"栏目中的"百宝箱"互动环节，是一种竞猜游戏，游戏规则如下：在20个商标中，有5个商标牌的背面注明了一定的奖金额，其余商标的背面是一张苦脸，若翻到它就不得奖．参加这个游戏的观众有三次翻牌的机会．某观众前两次翻牌均得若干奖金，如果翻过的牌不能再翻，那么这位观众第三次翻牌获奖的可能性是多少
<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">20 - 2</gadget>
<output>18</output>

<gadget id="calculator">3 / 18</gadget>
<output>1/6 = around 0.166667</output>

<result>1/6 = around 0.166667</result>