Final answer:
To find the number of new students who joined the class, multiply the class size by the percentage of female students last week.
Step-by-step explanation:
To find the number of new students who joined the class, we need to compare the percentage of females in the class both last week and one week later. Let's assume that the percentage of females in the class last week was 60%. If the probability of selecting a female student is the same as last week, then we can use this percentage to find the number of females in the class this week.
If the current class size is 45 students, then the number of female students can be found by multiplying the class size by the percentage of female students:
Number of female students = 45 x 0.60 = 27
Since we assumed that the probability of selecting a female student is the same as last week, the number of female students must remain the same. Therefore, 27 female students joined the class.