From a bunch of four keys, three particular keys have to be used to open a combination lock, such that the second key can be used only after the first key and the third key can be used only after the second key. What are the chances of opening the lock in a random selection of three keys? Choose the correct choice.
A) 1/24
B) 1/36
C) 1/60
D) 1/80
E) 1/120
The probability is 1/4*1/3*1/2 = 1/24.   The answer is 1/24.
<result>A</result>
From a bunch of four keys, three particular keys have to be used to open a combination lock, such that the second key can be used only after the first key and the third key can be used only after the second key. What are the chances of opening the lock in a random selection of three keys?