Answer:
The probability that the teacher calls upon a boy is, 0.5714.
Explanation:
The data provided is:
Boys Girls Total
Wilmette 11 7 18
Winnetka 5 4 9
Glencoe 4 4 8
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Total 20 15 35
The total number of students is, N = 35.
The number of boys in the class is, n (B) = 20
The probability of an event E is:

Compute the probability of selecting a boy as follows:

Thus, the probability that the teacher calls upon a boy is, 0.5714.