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Nookie1986 [14]
3 years ago
15

In order to officailly bid on a contract, a contractor wants to be 95% confident that his error is less than two hours in estima

ting 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?
Mathematics
1 answer:
iVinArrow [24]3 years ago
4 0

Answer: 20

Step-by-step explanation:

Formula to find the sample size : n=(\dfrac{\sigma\times z_{\alpha/2}}{E})^2

Given : Significance level : \alpha=1-0.95=0.05

Critical value : z_{\alpha/2}=1.96

Margin of error : E

Standard deviation: \sigma=\text{ 4.5 hours}

Then, we have

n=(\dfrac{4.5\times(1.96)}{2})^2=19.4481\approx20

Hence, the minimum sample size must be 20.

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