In a class of 28 students, 11 have a brother and 9 have a sister. There are 2 students who have a brother and a sister. What is the probability that a student has a sister
given that they have a brother?

Step-by-step explanation:

Conditional Probability

Is a measure of the probability of the occurrence of an event, given that another event has already occurred. If event B has occurred, then the probability that event A occurs is given by:

Where is the probability that both events occur and P(B) is the probability that B occurs.

Let's define events A and B for the question. There are 11 students that have a brother and 9 that have a sister. Two of those students have a brother and a sister.

We are given the fact that the selected student has a brother: this is the event that has already occurred, thus:

B = A student has a brother

A = A student has a sister

The probability that a student has a brother is:

The probability that the student has a brother and a sister is:

Thus, the conditional probability is:

Simplifying:

13

step-by-step explanation:

divide the cost of the total of sodas you bought by the cost of one soda, for example:

$24.57 divided by $1.89 is 13 which means you bought 13 sodas