# The atomic weight of a reference sample of silver was measured at the National Institute of Standards

## Question:

The atomic weight of a reference sample of silver was measured at the National Institute of Standards and Technology (NIST) using two nearly identical mass spectrometers. This project was undertaken in conjunction with the redetermination of the Faraday constant. Following are 48 observations:

Notice that the data differ only in the fifth, sixth, and seventh decimal places. Most computers will round the data and their calculated results; thus, the variation is seemingly lost. The statistics can be computed using just the last three digits of each data value (i.e., 107.8681568 will become 568). Algebraically this coding looks like this: Atom Wt Coded = (Atomic weight =107.8681000) Ã—10,000,000 The data are listed in both the original and coded formats at cengagebrain.com.
a. Construct a graph of the coded dat
a. How does the coding appear on the graph?
b. Find the mean and standard deviation of the coded data.
c. Convert the answers found in part b to original units.
d. Determine whether the data have an approximately normal distribution. Present your case.
e. Do the SDSM and CLT apply? Explain.
f. Is sigma known?
g. If the goal is to find the 95% confidence interval for the mean value of all observations, what would you do?
h. Find the 95% confidence interval for the mean value of all such observations. Justify your method.

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