Question

Which of the following is not a complementary event?

• A. Probability of finding a student inside or outside the class on a school day.
• B. Probability of finding red balls in a bag having green and red balls only.
• C. Probability that the topper of the school is boy or a girl (if only two sexes are considered).
• D. None of these

Answer 1

The correct option is D

None of these

Complementary events are two different outcomes of an event that are the only two possible outcomes for that event.
For e.g.
1. In the case of flipping of a coin, the only two possible outcomes are head and tails. Thus flipping of a coin is a complementary event.
2. On a school day, a student can either be found either inside the class or outside the class.
Thus, these are the only two possible outcomes. Hence, this event is a complementary event.
3. If a bag has only green and red balls, then there are only two possible outcomes: either the selected ball will be red or green.
Thus this also is a complementary event.
4. The topper of a school can either be a girl or a boy if only two sexes are considered. Thus this event is also complementary.