In a medical examination of students of a class, the following blood groups are recorded.
Blood groupA+AB−B−O+Number of1013125students
A student is selected at random from the class. The probability that he/she has blood group B− is:
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Solution
Total number of students in the medical examination, n(S) = 40
Number of students who have B− blood group, n(E) = 12 ∴ Probability that he/she has blood group B−=n(E)n(S)=1240=310