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(a) The total set has 7+3+6 = 16 persons.
The probability to select a teacher at the 1-st selection is ;
The probability to select a teacher at the 2-nd selection is ;
The probability to select a teacher at the 3-rd selection is .
Therefore, the answer to (a) is the product ...
You compute it.
(b) By analogy,
The probability to select no teacher at the 1-st selection is , (where 9 = 3 + 6)
The probability to select no teacher at the 2-nd selection is ;
The probability to select no teacher at the 3-rd selection is .
Again, you compute it.
Solved, answered, explained and completed.