Based on the given information, we know that the mean starting salary of the job placement agency's clients last year was $40,000. Here's how we can evaluate each statement:
- This year at least one of their clients will have a starting salary of at least $40,000.
There is not enough information to determine whether this statement is true or false. The mean starting salary from last year does not provide information on this year's salaries.
- Last year some of their clients had a starting salary of exactly $40,000.
This statement is true. Since the mean includes all starting salaries, it is possible for some clients to have had a starting salary of exactly $40,000.
- Last year fewer than half of their clients had a starting salary of $40,000 or less.
This statement is false. Since the mean starting salary is $40,000, it is impossible for fewer than half of the clients to have had a starting salary of $40,000 or less.
- Last year some of their clients had a starting salary of more than $36,000.
This statement is true. Since the mean starting salary is $40,000, it is possible for some clients to have had a starting salary of more than $36,000.
- Last year at least one of their clients had a starting salary of at least $40,000.
This statement is true. Since the mean starting salary is $40,000, it is possible for at least one client to have had a starting salary of at least $40,000.
Therefore, the statements that must be true based on the given information are:
- Last year some of their clients had a starting salary of exactly $40,000.
- Last year some of their clients had a starting salary of more than $36,000.
- Last year at least one of their clients had a starting salary of at least $40,000.