# Statistics

Biologists studying the healing of skin wounds measured the rate at which new cells closed a razor cut made in the skin of an anesthetized newt. Here are data from 18 newts, measured in micrometers per hour: 29,27,34,40,22,28,14,35,26,35,12,30,23,18,11,22,23,33.
Questions: a)Scientists usually assume that animal subjects are SRSs from their species or genetic type. Treat these newts as an SRS and suppose you know that the standard deviation of healing rates for this species of newt is 8 micrometers per hour. Give a 90% confidence interval for the mean healing rate for the species.

First, calculate the mean of the 18 observations. You are given the SD at 8. Use a cumulative normal distribution table (probably in the back of your stats text). Find the appropriate factor for a 90% confidence interval (hint: your interval should reflect a 2-tailed test). Call this factor U. 90% confidence would be (mean - 8*U) to (mean + 8*U)

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