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Calculate the upper and lower limit for a 95% confidence interval about this mean. a family needs a new car, but isn't sure they can fit the payment into their budget. a sample of 36 months of grocery bills yields a mean of $94 with a standard deviation of $10. if the upper limit of a 95% confidence level is below $100, the family can afford to buy the car. standard error = (standard deviation)/(square root of sample size) upper limit (dollars and cents) lower limit (dollars and cents)

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Kalahira
Answer: Where:
θ = confidence value
n = number of observations
μ = mean
Θ = standard deviation
... then your interval will be:
μ - θΘ/√n ≤ X ≤ μ - θΘ/√n
For some reason they want you to calculate the standard error, which is the Θ/√n section, and I mentioned the 1.96 value, so the above equation simplifies to: μ - 1.96SE ≤ X ≤ μ - 1.96SE

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