Map Sapling Learning macmillan learning Using graphite furnace atomic absorption

Question

Map Sapling Learning macmillan learning Using graphite furnace atomic absorption spectrometry, the mean cadmium (Cd2) content value in a homogenized sample of 40 zebra mussles was found to be 2.80 ppb Cd2 with a standard deviation (s) of 0.60 ppb Cd2+ (assume that s is a good approximation of . Calculatethe 90% and 95% confidence intervals (CI) for: (A) two analyses and (B) five analyses of this homogenized sample. Number Number (A) 90 % CI = 2.80 ±112.68 | ppb 95 % CI = 2.80 ±115.39 ppb Number Number (B) 90 % CI = 2.80 ±10.57 | ppb 95% CI = 2.80±10.74 ppb

Explanation / Answer

For small sample size, and known sample standard deviation, use, 1-sample t interval.

A. The 90% c.i for two analyses is as follows:

xbar+-t(s/sqrt N), where, xbar is sample mean, t is t critical at alpha/2, df=n-1 and s is sample standard deviation, N is sample size.

=2.80+-6.31(0.60/sqrt 2)

=2.80+-2.68

Using the same formula the 95% c.i is as follows:

2.80+-12.71(0.60/sqrt 2)

=2.80+-5.39

B) Using the same formula, with sample size, N=5, the c.i is as follows:

The 90% c.i=xbar+-t(s/sqrt N)

=2.80+-2.13(0.60/sqrt 5)

=2.80+-0.57

The 95% c.i=2.80+-2.78(0.60/sqrt 5)

=2.80+-0.74

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