Use this excerpt to answer the following questions:

"Among the first 425 patients with confirmed Covid-19, the median age was 59 years and 56% were male. The majority of cases (55%) with onset before January 1, 2020, were linked to the Huanan Seafood Wholesale Market, as compared with 8.6% of the subsequent cases. The mean incubation period was 5.2 days (95% confidence interval [CI], 4.1 to 7.0), with the 95th percentile of the distribution at 12.5 days. In its early stages, the epidemic doubled in size every 7.4 days. With a mean serial interval of 7.5 days (95% CI, 5.3 to 19), the basic reproductive number was estimated to be 2.2 (95% CI, 1.4 to 3.9)."

1. The excerpt above includes "The mean incubation period was 5.2 days...". To calculate that mean, researchers added up the _____ and divided by ____. Re-write the sentence with filled-in blanks.

2. The excerpt above includes "...with the 95th percentile of the distribution at 12.5 days." Interpret the 12.5.

3. The excerpt above includes "The mean incubation period was 5.2 days (95% confidence interval [CI], 4.1 to 7.0)...". Explain the confidence interval.