A medical device company knows that the percentage of patients experiencing injection-site reactions with the current needle is 11%. What is the mean of X, the number of patients seen until an injection-site reaction occurs?

This is a geometric setting: each patient has a 0.11 probability of experiencing an injection-site reaction, and X counts patients until the first reaction. The mean waiting time is 1/p, so E(X) = 1/0.11 ≈ 9.0909 patients. Therefore, the mean is 9.0909, choice C.

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