Question

A couple is planning to have 3 children. Assuming that having a boy and having a girl are equally likely, and that the gender of one child has no influence on (or, is independent of) the gender of another, what is the probability that the couple will have exactly 2 girls? The "random experiment" in this case is having 3 children, as odd as that may sound in this context. The next and most important step is to determine what all of the possible outcomes are, and list them (i.e., list the sample space S). In this case, each outcome represents a possible combination of genders of 3 children (note that examples with the same number of boys and girls but a different birth order must be listed separately).

Answer 1

C or .375

Explanation:

Answer 2

44.444%, (B, B, B), (B, B, G), (B, G, B), (B, G, B), (B, G, G), (G, B, B), (G, B, G), (G, G, B), (G, G, G)

Explanation:

We will start with the second part of the question, listing out all of the possible combinations that can occur from this data set. There is a 50/50 chance of having a girl or a boy, and there are three children. For now we'll use B to represent a boy and G for a girl. It goes as follows:

(B, B, B), (B, B, G), (B, G, B), (B, G, B), (B, G, G), (G, B, B), (G, B, G), (G, G, B), (G, G, G)

I often find it easy to write out a branch diagram to help me visualize this problem and make sure I have all possibilities. (See attached image)

Count the total number of combinations (9). Next, count the number that include exactly 2 girls (4). With this information, we now know that there is a 4 out of 9 chance of having exactly 2 girls and one boy. 4/9 is in simplest form, so all you have to do is find the percentage (44.444%)