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muminat
3 years ago
7

Provide an appropriate response. In order to efficiently bid on a contract, a contractor wants to be 95% confident that his erro

r is less than two hours in estimating the average time it takes to install tile flooring. Previous contracts indicate that the standard deviation is 4.5 hours. How large a sample must be selected?
a.19
b.4
c.5
d.20
Mathematics
1 answer:
lidiya [134]3 years ago
5 0

Answer:

d. 20

Step-by-step explanation:

Standard deviation is 4.5

Margin error for the problem is 2 hours

Probability 95%, that means that the siginficance level α is 1 – p

α = 1 – 0.95 = 0.05

margin of error (ME) can be defined as follows

ME = Z(α/2) * standard deviation/ √n

Where n is the sample size

Z(0.05/2) = Z(0.025)

Using a z table Z = 1.96

Now, replacing in the equation and find n

2 = 1.96 * 4.5/ √n

2 = 8.82/√n

√n = 8.82/2

√n = 4.41

n = 4.41^2

n = 19.44 ≈ 20

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