I'm having a problem with this question:

Record shows that the students in a certain university has mean IQ of 115 with a standard deviation of 10. A research conducted on 30 students showed a mean IQ of 110. What is the probability that the sample of 30 students will have a mean IQ less than 115?

Our class came up with 3 different answers:

A.) .9969
They computed this using 110 as the population mean. [(115-110) / (10/√30)] then z-table.

B.) .0031
They computed this using 115 as the population mean then 110 as the random variable. [(110-115) / (10/√30)] then z-table.

C.) .5000
They computed this using 115 as the population mean then 115 as the random variable. [(115-115) / (10/√30)] then z-table.

In the end, our class accepted A as the answer but I'm not convinced. What are your thoughts about this?