There are 26 students in a class, 7 have blonde hair, 9 have glasses and 4 have both blond hair and glasses. If a student is selected at ran

The problem is to find how many students have either blond hair or glasses and then divide that by the total number of students; that will find the probability.

Since 7 have blonde hair and 9 have glasses, that would be a total of 16 persons if there were no overlap; that is, no blonde wears glasses and nobody who wears glasses is a blonde.

But there are 4 persons who have both blond hair and wears glasses. That means, of the 7 who are blondes, 3 of them do not wear glasses. And, of the 9 who wear glasses, 5 of them are not blondes.

So we have 3 who are blondes without glasses, 5 who wear glasses who are not blondes, and 4 blonds with glasses, for a total of 12 persons.

The probability is, therefore, 12/26 or 6/13.

16 out of 20

(I'm assuming you meant "20" students, rather than "26")

Let A be the probability that a student  has blonde hair  = 7/20 = P(A)

Let B be the probability that a student wears glasses = 9/20  = P(B)

And the probabilty that a student has both = 4/20 = P(A ∩ B)

So, the probability  that a student has either blonde hair or glasses = P(A ∪ B),  is gven by

P(A ∪ B) = P(A) + P(B) - P(A ∩ B) = 7/20 + 9/20 - 4/20 = 12/20

Go with geno's answer...it's better than mine !!! (We actually could have 26 students !!!)