Question Video: Determining the Probability of Complement of a Given Event Mathematics • Third Year of Preparatory School

Video Transcript

In a class, the probability that a student chosen at random is a girl is 0.34. What is the probability that a student chosen at random is not a girl?

The probability of 𝐴 plus the probability of 𝐴 dash must equal one. This means that the probability of an event occurring plus the probability of the event not occurring equal one.

In our example, the probability of choosing a girl plus the probability of choosing a student that is not a girl is equal to one. As we know, the probability of choosing a girl is 0.34. We can write this as an equation. 0.34 plus 𝑥 is equal to one. Subtracting 0.34 from both sides of this equation gives us 𝑥 is equal to 0.66.

This means that the probability of choosing a student at random that is not a girl is 0.66.