Over the past several months, an adult patient has been treated for tetany (severe muscle spasms). This condition is associated with an average total calcium level below 6 mg/dl. Recently, the patient's total calcium tests gave the following readings (in mg/dl). Assume that the population of x values has an approximately normal distribution.

Question

9.3 9.0 10.3 8.9 9.4 9.8 10.0 9.9 11.2 12.1
(a) Use a calculator with mean and sample standard deviation keys to find the sample mean reading x and the sample standard deviation s. (Round your answers to two decimal places.)
x =______ mg/dl
s = _______ mg/dl

(b) Find a 99.9% confidence interval for the population mean of total calcium in this patient's blood. (Round your answer to two decimal places.)
lower limit _______ mg/dl
upper limit _______ mg/dl

Answer 1

Do not have calculator.

(a) Find the mean first = sum of scores/number of scores

Subtract each of the scores from the mean and square each difference. Find the sum of these squares. Divide that by the number of scores to get variance.

Standard deviation = square root of variance

(b) Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (±.0005) and its Z score.

99.9% = mean ± Z SEm

SEm = SD/√n

Answer 2

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