The answer is
8
Root of 7
1/2
20
Given a table below which gives the years in A.D. for an archaeological excavation site using the method of tree ring dating:

Part A:
The sample mean is given by:

Therefore, the sample mean is 1268.
Part B:
We calculate the sample standard deviation as follows:

Part C:
The 90% confidence interval is given by:
Reflect across the y axis and moved through the translation x = 2