What is the standard deviation?

Question by ether: What is the standard deviation?
Suppose the length of time to onset of lung cancer in asbestos workers is approximately normally distributed with a mean of 26 years and a variance of 4 years squared.

a. What is the standard deviation?

b. What interval of onset times includes about 95% of the workers?
Approximate using empirical rule.

c. Find the exact value for the interval in (b) using z table or z* from t table.

d. What is the probability that an

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