A school psychologist administered the Stanford-Binet intelligence quotient (IQ) test in two counties. Forty randomly selected gifted and talented students were selected from each county. The Stanford-Binet IQ test is said to follow a normal distribution with a mean of 100 and standard deviation of 16. The data collected are stored in the data frame SBIQ.
(a) Although the standard deviation for the Stanford-Binet IQ test is known, should it be used? Justify.
(b) Be careful, the confidence interval formula that should be used in this situation has not been explicitly covered yet. Construct a 90% confidence interval for the true average IQ difference for gifted and talented students between the two counties.
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