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4 years ago

Last summer, Betty earned $4200 by painting houses. She invested

Mathematics

1 answer:

Musya8 [376]4 years ago

3 0

x*(1.035) + (4,200-x)*(1.045) = 4,374.00

1.035x + 4,389.00 -1.045x = 4,374.00

15.00 = .01x

x = 1,500 so x (1,500) invested at 3.5% and

(4,200 - 1,500) (or 2,700) invested at 4.5%

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In 2009 a survey of Internet usage found that 79 percent of adults age 18 years and older in the United States use the Internet.

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$0.025 = 2.33\sqrt{\frac{0.79*0.21}{n}}$

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Step-by-step explanation:

In a sample with a number n of people surveyed with a probability of a success of $\pi$ , and a confidence level of $1-\alpha$ , we have the following confidence interval of proportions.

$\pi \pm z\sqrt{\frac{\pi(1-\pi)}{n}}$

In which

z is the zscore that has a pvalue of $1 - \frac{\alpha}{2}$ .

The margin of error is:

$M = z\sqrt{\frac{\pi(1-\pi)}{n}}$

79 percent of adults age 18 years and older in the United States use the Internet.

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98% confidence level

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Which of the following should be used to find the sample size (n) needed?

We have to find n for which $M = 0.025$

So the equation is:

$M = z\sqrt{\frac{\pi(1-\pi)}{n}}$

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Option d.

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