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4 years ago

12

An article claims that 12% of trees are infested by a bark beetle. A random sample of 1,000 trees were tested for traces of the

infestation and found that 127 trees were affected.
z = p - p/p q/n
Using the formula and data provided, what is the value of the z-test statistic?

1 answer:

inna [77]4 years ago

7 0

Answer: 0.6812

Step-by-step explanation:

Let p be the population proportion of trees are infested by a bark beetle.

As per given: p= 12%= 0.12

Sample size : n= 1000

Number of trees affected in sample = 1000

Sample proportion of trees are infested by a bark beetle. = $\hat{p}=\dfrac{127}{1000}=0.127$

Now, the z-test statistic : $z=\dfrac{\hat{p}-p}{\sqrt{\dfrac{p(1-p)}{n}}}$

So, $z=\dfrac{0.127-0.12}{\sqrt{\dfrac{0.12\times 0.88}{1000}}}$

$z=\dfrac{0.007}{\sqrt{\dfrac{0.1056}{1000}}}\\\\\\=\dfrac{0.007}{\sqrt{0.0001056}}\\\\\\=\dfrac{0.007}{0.010276}\approx0.6812$

Hence, the value of the z-test statistic = 0.6812 .

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Find the inverse of the function.<br> y = X - 9

djyliett [7]

Answer:

x=y+9

Step-by-step explanation:

so what we do here is take x-9 and add 9 to both sides giving us y+9=x all we do is put x first and y+9 last and we have the inverse

8 0

4 years ago

Will someone please help me

Rufina [12.5K]

Answer:

The filled table for each equation by using the exact values in the table is

10x+2y=56

x y

______________________

0 28

$\frac{56}{10}$ 0

________________________

8x+3y=49

x y

_________________________

0 $\frac{49}{3}$

$\frac{49}{8}$ 0

_________________________

Step-by-step explanation:

Given equations are 10x+2y=56 and 8x+3y=49

To fill the table for each equation by using the exact values in the table :

10x+2y=56

put x=0 in above equation we get

10(0)+2y=56

2y=56

$y=\frac{56}{2}$

$y=28$

Therefore (0,28)

put y=0 in the given equation 10x+2y=56 we get

10x+2(0)=56

10x=56

$x=\frac{56}{10}$

Therefore ( $\frac{56}{10}$ ,0)

10x+2y=56

x y

_________________________

0 28

$\frac{56}{10}$ 0

__________________________

For

8x+3y=49

put x=0 in above equation we get

8(0)+3y=49

3y=49

$y=\frac{49}{3}$

Therefore (0, $\frac{49}{3}$ )

put y=0 in the given equation 8x+3y=49 we get

8x+3(0)=49

8x=49

$x=\frac{49}{8}$

Therefore ( $\frac{49}{8}$ ,0)

8x+3y=49

x y

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0 $\frac{49}{3}$

$\frac{49}{8}$ 0

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7 0

4 years ago

23. A certain type of gasoline is supposed to have a mean octane rating of at least 90. Suppose measurements are taken on of 5 r

Nostrana [21]

Answer:

a) $p_v =P(Z$

b) Since $p_v$ we can reject the null hypothesis at the significance level given. So based on this we can commit type of Error I.

Because Type I error " is the rejection of a true null hypothesis".

c) $P(\bar X >90)=1-P(Z$

$1-P(Z$

d) For this case we need a z score that accumulates 0.02 of the area on the right tail and 0.98 on the left tail and this value is z=2.054

And we can use this formula:

$2.054=\frac{90-89}{\frac{0.8}{\sqrt{n}}}$

And if we solve for n we got:

$n = (\frac{2.054 *0.8}{1})^2=2.7 \approx 3$

Step-by-step explanation:

Previous concepts and data given

The margin of error is the range of values below and above the sample statistic in a confidence interval.

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

We can calculate the sample mean and deviation with the following formulas:

$\bar X = \frac{\sum_{i=1}^n X_i}{n}$

$s=\sqrt{\sum_{i=1}^n (X_i -\bar X)^2}{n-1}$

$\bar X=88.96$ represent the sample mean

$s=1.011$ represent the sample standard deviation

n=5 represent the sample selected

$\alpha$ significance level

State the null and alternative hypotheses.

We need to conduct a hypothesis in order to check if the mean is less than 90, the system of hypothesis would be:

Null hypothesis: $\mu \geq 90$

Alternative hypothesis: $\mu < 90$

If we analyze the size for the sample is < 30 and we don't know the population deviation so is better apply a t test to compare the actual mean to the reference value, and the statistic is given by:

$z=\frac{\bar X-\mu_o}{\frac{\sigma}{\sqrt{n}}}$ (1)

z-test: "Is used to compare group means. Is one of the most common tests and is used to determine if the mean is (higher, less or not equal) to an specified value".

Calculate the statistic

We can replace in formula (1) the info given like this:

$z=\frac{88.96-90}{\frac{0.8}{\sqrt{5}}}=-2.907$

Part a

P-value

First we need to calculate the degrees of freedom given by:

$df=n-1=5-1 = 4$

Then since is a left tailed test the p value would be:

$p_v =P(Z$

Part b

Since $p_v$ we can reject the null hypothesis at the significance level given. So based on this we can commit type of Error I.

Because Type I error " is the rejection of a true null hypothesis".

Part c

We want this probability:

$P(\bar X$

The best way to solve this problem is using the normal standard distribution and the z score given by:

$z=\frac{x-\mu}{\frac{\sigma}{\sqrt{n}}}$

If we apply this formula to our probability we got this:

$P(\bar X >90)=1-P(Z$

$1-P(Z$

Part d

For this case we need a z score that accumulates 0.02 of the area on the right tail and 0.98 on the left tail and this value is z=2.054

And we can use this formula:

$2.054=\frac{90-89}{\frac{0.8}{\sqrt{n}}}$

And if we solve for n we got:

$n = (\frac{2.054 *0.8}{1})^2=2.7 \approx 3$

7 0

3 years ago

(High points) please solve with explanation

AysviL [449]

Answer:

The area and the perimeter of the picture are:

<u>Area = 160 cm^2</u>
<u>Perimeter = 67.31 cm</u>

Step-by-step explanation:

To find the area of that figure, you can find the area how if it was a rectangle and next subtract the area of the triangle in the upper part. The area of a rectangle could be found by the next formula:

Area of a rectangle = base * height

As you can see in the picture, the base is 16 cm and the height is 12 cm, then we replace in the formula:

Area of a rectangle = 16 cm * 12 cm
Area of a rectangle = 192 cm^2

Now, we calculate the area of the triangle to subtract to the area we found and obtain the real area, the formula to obtain the area of a triangle is:

Area of a triangle = (base * height) / 2

The height of the triangle is 8 cm, and the base is 8 cm too, because you subtract to the base of the rectangle (16 cm) the measurements in the upper part (16 - 4 - 4 = 8), Now, we replace in the formula:

Area of a triangle = (8 cm * 8 cm) / 2
Area of a triangle = (64 cm^2) / 2
Area of a triangle = 32 cm^2

We subtract to the found area:

Area of the picture = 192 cm^2 - 32 cm^2
<u>Area of the picture = 160 cm^2</u>

To find the perimeter, you must add all the sides of the picture, but, as you can see, there is a side that doesn't have the measurent, this is the hypotenuse of the triangle used before, but how we know the other sides, we can use Pythagorean theorem:

$a^{2}+b^{2}=c^{2}$

Where:

a = Opposite leg (8 cm)
b = Adjacent leg (8 cm)

So, we replace in the theorem:

$a^{2}+b^{2}=c^{2}$

$(8 cm)^{2}+(8cm)^{2}=c^{2}$ (and we clear c)
$\sqrt{(8 cm)^{2}+(8cm)^{2}} =c$
$\sqrt{64 cm^{2}+64cm^{2}} =c$
$\sqrt{128cm^{2}} =c$
c = 11.3137085 cm
c ≅ 11.31 cm

At last, we add all the sides of the picture begining by the base and going by the left side:

Perimeter of the picture = 16 cm + 12 cm + 4 cm + 11.31 cm + 8 cm + 4 cm + 12 cm
<u>Perimeter of the picture = 67.31 cm approximately</u>.

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3 years ago

Owen has a loan for $3700 at a rate of 5% annually. If the interest is not compounded, what is the total amount of repayment if

Jobisdone [24]

Not sure sorry

Edit: oh sorry I didn’t mean to write that

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3 years ago