### Video Transcript

A class contains six boys and 21 girls. What is the probability of selecting a girl if a student is selected at random?

We begin by recalling that probability is the likelihood or chance of an event occurring. We know that the probability of an event occurring can be written as a fraction where the numerator is the number of favorable outcomes and the denominator is the total number of outcomes.

In this question, we need to find the probability of selecting a girl if a student is selected at random. We are told that there are 21 girls, so our numerator will be 21. There are six boys, and six plus 21 is equal to 27. As there are 27 students altogether, the probability of selecting a girl is 21 out of 27. Both the numerator and denominator are divisible by three, so we can simplify our fraction. 21 divided by three is equal to seven, and 27 divided by three is equal to nine. If a student from the class is selected at random, the probability of selecting a girl is seven out of nine or seven-ninths.