Answer:
1/6
Explanation:
The number of ways they can line up is 3×2×1 = 6. Only one of these is alphabetical order. The probability that they will line up randomly in alphabetical order is 1/6.
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Any of the three can line up first; either of the remaining two can line up second, and the remaining person can line up last. Thus there are 3×2×1 possible orders.