SOLUTION: In a survey, 21 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $40 and standard deviation of $19. C

Question 1189932: In a survey, 21 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $40 and standard deviation of $19. Construct a 90% confidence interval in the form: Estimate ± margin of error.
Answer by math_tutor2020(3817) (Show Source): You can put this solution on YOUR website!

Given info:
n = 21 = sample size
xbar = 40 = sample mean
s = 19 = sample standard deviation
C = 0.90 = 90% = confidence level

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Use a calculator or table to find the T critical value based on these inputs

df = degrees of freedom = n-1 = 21-1 = 20
confidence level = 90%

You should find that the T critical value is roughly t = 1.725

The point estimate is the sample mean (40) which estimates the population mean (mu).

The margin of error (MoE) is
MoE = t*s/sqrt(n)
MoE = 1.725*19/sqrt(21)
MoE = 7.15209135248464
MoE = 7.15

Answer: 40 ± 7.15

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