WAEC Mathematics 2017 Objective — Question 32

Question 32 of 50 from the West African Examinations Council (WAEC) Mathematics 2017 Objective paper, with the correct answer and a full explanation.

In a class of 45 students, 28 offer Chemistry and 25 offer Biology. If each student offers at least one of the two subjects, calculate the probability that a student selected at random from the class offers Chemistry only.

A. A. 2/9
B. B. 4/9Correct
C. C. 5/9
D. D. 7/9

Explanation

Let x = number offering both. 28-x+25-x+x=45 → 53-x=45 → x=8. Only Chemistry = 28-8=20. P(only Chemistry)=20/45=4/9.

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