Operations research
See attached image for details. The use of statistical software such as maple is encouraged.
Answer
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The average number of arrival is 20 students every 15 minutes.

There is s typo in the second equation. The number 320 in both places should be replaced by 20.

The final answer 11.218% is of course correct.

Thanks for the answer you seem to understand this well. I have posted another question on an M/M/c queuing model, do you think you could answer that?
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