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# Finding the critical value t* for a desired confidence level

AP.STATS: UNC‑4 (EU), UNC‑4.Q (LO), UNC‑4.Q.1 (EK)
You might need: Calculator,t table

## Problem

Emilio took a random sample of n, equals, 12 giant Pacific octopi and tracked them to calculate their mean lifespan. Their lifespans were roughly symmetric with a mean of x, with, \bar, on top, equals, 4 years and a standard deviation of s, start subscript, x, end subscript, equals, 0, point, 5 years. He wants to use this data to construct a t interval for the mean lifespan of this type of octopus with 90, percent confidence.
What critical value t, start superscript, times, end superscript should Emilio use?