Question 1135844
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There are two (TWO) groups of students under the consideration.


First group (let's call it A) consists of nine brown-eyed and three blue-eyed brunettes.


Second group (let's call it B) consists of two blue-eyed and three brown-eyed children with black hair.


Since the chosen student is a brunette, it means that he (or she) was chosen among the group A.


The probability to choose a child with brown eyes among the group A is  {{{9/(9+3)}}} = {{{9/12}}} = {{{3/4}}} = 0.75 = 75%.   <U>ANSWER</U>
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Solved.