Question 1119031
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Let X be the total number of students in the group.


Then the number of females is 0.6X, while the number of males is 0.4X.


The number of females with short hair is 0.7*(0.6X) = 0.42X,       (<<<---=== 0.7 = 1-0.3 )


while the number of males with short hair is 0.8*(0.4X) = 0.32X.   (<<<---=== 0.8 = 1-0.2 )


Thus the total number of individuals with short hair is  0.42X + 0.32X = 0.74X.


Then the probability under the question is {{{(0.74X)/X}}} = 0.74 = 74%.
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Solved.