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Darina [25.2K]
3 years ago
14

At a particular academically challenging high school, the average gpa of a high school senior is known to be normally distribute

d. after a sample of 20 seniors is taken, the average gpa is found to be 2.71 and the variance is determined to be 0.25. find a 90% confidence interval for the population mean gpa.
Mathematics
2 answers:
valentina_108 [34]3 years ago
8 0

Answer:

The 90% confidence interval for the population mean gpa is [2.526,2.894].

Step-by-step explanation:

The confidence interval for population mean is

\mu\pm z^{*}\cdot \frac{\sigma}{\sqrt{n}}

Where, μ is population mean, σ is standard deviation, z* is the value of z-score and n is number of samples.

The z-score value for 90% confidence interval is 1.645.

The average gpa is found to be 2.71, so μ=2.71. The variance is 0.25, it means

\sigma^2=0.25

\sigma=0.5

The 90% confidence interval for population mean is

2.71\pm 1.645\cdot \frac{0.5}{\sqrt{20}}

[2.71-1.645\cdot \frac{0.5}{\sqrt{20}},2.71+1.645\cdot \frac{0.5}{\sqrt{20}}]

[2.526,2.894]

Therefore the 90% confidence interval for the population mean gpa is [2.526,2.894].

brilliants [131]3 years ago
7 0

Solution: The 90% confidence interval for the population mean is:

\bar{x} \pm t_{\frac{0.1}{2}} \frac{s}{\sqrt{n}}

Where:

\bar{x}=2.71

s=\sqrt{0.25} =0.5

t_{\frac{0.1}{2}}=1.729 is the critical value at 0.1 significance level for df = n-1 =20-1=19

2.71 \pm 1.729 \frac{0.5}{\sqrt{20}}

2.71 \pm0.19

\left( 2.71-0.19,2.71+0.19\right)

\left(2.52,2.90 \right)

Therefore, the 90% confidence interval for the population mean is \left(2.52,2.90 \right)


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