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AfilCa [17]
2 years ago
13

You are interested in estimating the the mean age of the citizens living in your community. In order to do this, you plan on con

structing a confidence interval; however, you are not sure how many citizens should be included in the sample. If you want your sample estimate to be within 5 years of the actual mean with a confidence level of 94%, how many citizens should be included in your sample? Assume that the standard deviation of the ages of all the citizens in this community is 22 years.
Mathematics
1 answer:
Naddika [18.5K]2 years ago
8 0

Answer:

The sample size is    n = 68

Step-by-step explanation:

From the question we are told that

    The margin of error is  E = 5 \ years

     The standard deviation is  \sigma = 22

From the question we are told the confidence level is  94% , hence the level of significance is    

      \alpha = (100 - 94 ) \%

=>   \alpha = 0.06

Generally from the normal distribution table the critical value  of  \frac{\alpha }{2} is  

   Z_{\frac{\alpha }{2} } =  1.881

Generally the sample size is mathematically represented as  

   n = [\frac{Z_{\frac{\alpha }{2} } *  \sigma }{E} ] ^2

=>  n = [\frac{1.881 } *  22 }{5} ] ^2

=>  n = 68

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Doss [256]

Answer:

(a) V = -H^3+ 5H^2 + 36H

(b) Length = 5in; Width = 9in; Height = 5in or Length = 3in; Width = 10in; Height = 6in

Step-by-step explanation:

Let:

W=Width; L = Length; H = Height

Given

W = 4 + H

L = 9 - H

Solving (a): The polynomial for the volume in terms of height

Volume (V) is calculated using:

V = L * W * H

V = (9 - H) * (4 + H) * H

Expand

V = (9 - H) * (4H + H^2)

Open brackets

V = 36H + 9H^2 - 4H^2 - H^3

V = 36H + 5H^2 - H^3

Rewrite as:

V = -H^3+ 5H^2 + 36H

Solving (b): The dimensions when Volume = 180

Substitute 180 for V in: V = -H^3+ 5H^2 + 36H

180 = -H^3+ 5H^2 + 36H

Rewrite as:

H^3 - 5H^2 - 36H + 180 = 0

Factorize:

H^2(H - 5) - 36(H - 5) = 0

(H^2 - 36)(H - 5) = 0

Express H^2 - 36 as difference of two squares

(H - 6)(H + 6)(H - 5) =0

This gives:

H - 6 =0==> H = 6

H + 6 =0==> H = -6

H - 5 =0==> H = 5

Since the height can not be negative, then H = 5 or H = 6

Recall that:

W = 4 + H

L = 9 - H

When H = 5

W = 4 + 5 = 9

L = 9 - 5 = 4

When H = 6

W = 4 + 6 = 10

L = 9 - 6 = 3

Hence, the dimensions of the box are:

Length = 5in; Width = 9in; Height = 5in

or

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Step-by-step explanation:

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Step-by-step explanation:

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