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lawyer [7]
3 years ago
9

X-y=3 X+2y=-6 Solve using substitution

Mathematics
1 answer:
Tresset [83]3 years ago
3 0
X-y=3=>x=3+y
X+2y=-6
=========
3+y+2y=-6
3+3y=-6
3y=-6-3
3y=-9
y=-3

X+2y=-6
X+2(-3)=-6
X-6=-6
X=0
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At a large Midwestern university, a simple random sample of 100 entering freshmen in 1993 found that 20 of the sampled freshmen
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Answer:

The 90% confidence interval for the difference of proportions is (0.01775,0.18225).

Step-by-step explanation:

Before building the confidence interval, we need to understand the central limit theorem and subtraction of normal variables.

Central Limit Theorem

The Central Limit Theorem establishes that, for a normally distributed random variable X, with mean \mu and standard deviation \sigma, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean \mu and standard deviation s = \frac{\sigma}{\sqrt{n}}.

For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.

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Subtraction between normal variables:

When two normal variables are subtracted, the mean is the difference of the means, while the standard deviation is the square root of the sum of the variances.

p1 -> 1993

20 out of 100, so:

p_1 = \frac{20}{100} = 0.2

s_1 = \sqrt{\frac{0.2*0.8}{100}} = 0.04

p2 -> 1997

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p_2 = \frac{10}{100} = 0.1

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Confidence interval:

p \pm zs

In which

z is the z-score that has a p-value of 1 - \frac{\alpha}{2}.

90% confidence level

So \alpha = 0.1, z is the value of Z that has a p-value of 1 - \frac{0.1}{2} = 0.95, so Z = 1.645.  

The lower bound of the interval is:

p - zs = 0.1 - 1.645*0.05 = 0.01775&#10;

The upper bound of the interval is:

p + zs = 0.1 + 1.645*0.05 = 0.18225&#10;

The 90% confidence interval for the difference of proportions is (0.01775,0.18225).

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Answer:

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Step-by-step explanation:

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