a) Scores on the mathematics part of the SAT exam in a recent year were roughly Normal with mean 455 and standard deviation 104. You choose an SRS of 100 students and average their SAT math scores. If you do this many times, with a sample of size 100 each time, the mean of the average scores will get close to A. 45.5 B. 455 C. 4.55 D. None of the above.
a) Scores on the mathematics part of the SAT exam in a recent year were roughly Normal with
A. 45.5
B. 455
C. 4.55
D. None of the above.
(b) A newborn baby has extremely low birth weight (ELBW) if it weighs less than 1000 grams. A study of the health of such children in later years examined a random sample of 219 children. Their mean weight at birth was x¯=x¯= 810 grams. This sample mean is an unbiased estimator of the mean weight μμ in the population of all ELBW babies. This means that
A. the sample mean x¯x¯ is always equal to μμ.
B. the sample mean x¯x¯ will have a distribution that is close to Normal.
C. the average sample mean x¯x¯, over all possible samples, is equal to μμ.
D. None of the above.
(c) The length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266 days and standard deviation 16 days. The probability that the average pregnancy length for 6 randomly chosen women exceeds 270 days is about
A. 0.07
B. 0.27
C. 0.4
D. None of the above
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