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- Total number of possible arrangements of the five surnames = 5! = 120.

- Favorable Outcomes are arrangements where 3 names are in correct positions and 2 are in incorrect positions.


Example to visualize this

Say, the correct alphabetical-order arrangement of the names is A-B-C-D-E.

We need to find the number of arrangements where exactly two names are swapped.

Example: A-D-C-B-E.


Observe: In effect, we need to find the number of arrangements where exactly 3 names are in correct positions and 2 are in incorrect positions

This is 5C3 (to choose the names in correct positions) x 2C2 (to choose the names that are not in correct positions) = 10 x 1 = 10.

Our answer: Favorable/Total = 10/120 = 1/12. Choice B.
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