Listed in the data table are amounts of strontium-90 (in millibecquerels. or mBq

Question

Listed in the data table are amounts of strontium-90 (in millibecquerels. or mBq. per gram of calcium) in a simple random sample of baby teeth obtained from residents in two cities. Assume that the two samples are independent simple random samples selected from normally distributed populations. Do not assume that the population standard deviations are equal. Construct a confidence interval suitable for testing the claim that the mean amount of strontium-90 from city #1 residents is greater than the mean amount from city #2 residents. Your answer should use interval notation. (Round to two decimal places as needed.)

Explanation / Answer

from above

degree of freedom=((S12/n1+S22/n2)2/((s12/n1)2/(n1-1)+(s22/n2)2/(n2-1))=16

for std error = (S12/n1+S22/n2)1/2=22.625

for 95% CI and 16 degree of freedom t=2.1199

hence 95% CI =mean diff +/- t*std error =-10.212 ; 85.712

S. no sample 1 sample 2 110 117 86 68 121 100 115 85 101 85 104 107 213 110 134 111 290 114 100 133 274 101 145 209 total 1793.000 1340.000 mean 149.417 111.667 std deviation(S) 70.065 35.119

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