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3 years ago

What is the solution to y - 7 = -7? A. y = 14 B. y = 7 C. y = 0 D. y = -7

Mathematics

2 answers:

horrorfan [7]3 years ago

7 0

If you add 7 to negative 7, it would be y=0.

Answer: y=0

MrMuchimi3 years ago

7 0

C. y=0

Hope my answer helped

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Given the diagram below, what statement can you not make?

Vaselesa [24]

Answer:

b, 5=3

Step-by-step explanation:

4 0

3 years ago

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Eight year-old Alex is learning to ride a

cestrela7 [59]

Answer:

The age of the horse, in human years, when Alex was born can be determined by simply deducting the Current age of Alex from the Current age of the horse in human years.

Therefore, the age of the horse, in human years, when Alex was born was 42 years.

Step-by-step explanation:

Current age of Alex = 8

Current age of the horse in human years = 50

Since the age of the horse is already stated in human years, it implies there is no need to convert the age of the horse again.

Therefore, since Alex is a human who was born 8 years ago, the age of the horse, in human years, when Alex was born can be determined by simply deducting the Current age of Alex from the Current age of the horse in human years as follows:

The age of the horse, in human years, when Alex was born = 50 - 8 = 42

Therefore, the age of the horse, in human years, when Alex was born was 42 years.

This can be presented in a table as follows:

Age of Alex Age of the Horse (in human years)

Eight years ago 0 42

Current age 8 50

6 0

3 years ago

The lifetime X (in hundreds of hours) of a certain type of vacuum tube has a Weibull distribution with parameters α = 2 and β =

stich3 [128]

I'm assuming $\alpha$ is the shape parameter and $\beta$ is the scale parameter. Then the PDF is

$f_X(x)=\begin{cases}\dfrac29xe^{-x^2/9}&\text{for }x\ge0\\\\0&\text{otherwise}\end{cases}$

a. The expectation is

$E[X]=\displaystyle\int_{-\infty}^\infty xf_X(x)\,\mathrm dx=\frac29\int_0^\infty x^2e^{-x^2/9}\,\mathrm dx$

To compute this integral, recall the definition of the Gamma function,

$\Gamma(x)=\displaystyle\int_0^\infty t^{x-1}e^{-t}\,\mathrm dt$

For this particular integral, first integrate by parts, taking

$u=x\implies\mathrm du=\mathrm dx$

$\mathrm dv=xe^{-x^2/9}\,\mathrm dx\implies v=-\dfrac92e^{-x^2/9}$

$E[X]=\displaystyle-xe^{-x^2/9}\bigg|_0^\infty+\int_0^\infty e^{-x^2/9}\,\mathrm x$

$E[X]=\displaystyle\int_0^\infty e^{-x^2/9}\,\mathrm dx$

Substitute $x=3y^{1/2}$ , so that $\mathrm dx=\dfrac32y^{-1/2}\,\mathrm dy$ :

$E[X]=\displaystyle\frac32\int_0^\infty y^{-1/2}e^{-y}\,\mathrm dy$

$\boxed{E[X]=\dfrac32\Gamma\left(\dfrac12\right)=\dfrac{3\sqrt\pi}2\approx2.659}$

The variance is

$\mathrm{Var}[X]=E[(X-E[X])^2]=E[X^2-2XE[X]+E[X]^2]=E[X^2]-E[X]^2$

The second moment is

$E[X^2]=\displaystyle\int_{-\infty}^\infty x^2f_X(x)\,\mathrm dx=\frac29\int_0^\infty x^3e^{-x^2/9}\,\mathrm dx$

Integrate by parts, taking

$u=x^2\implies\mathrm du=2x\,\mathrm dx$

$\mathrm dv=xe^{-x^2/9}\,\mathrm dx\implies v=-\dfrac92e^{-x^2/9}$

$E[X^2]=\displaystyle-x^2e^{-x^2/9}\bigg|_0^\infty+2\int_0^\infty xe^{-x^2/9}\,\mathrm dx$

$E[X^2]=\displaystyle2\int_0^\infty xe^{-x^2/9}\,\mathrm dx$

Substitute $x=3y^{1/2}$ again to get

$E[X^2]=\displaystyle9\int_0^\infty e^{-y}\,\mathrm dy=9$

Then the variance is

$\mathrm{Var}[X]=9-E[X]^2$

$\boxed{\mathrm{Var}[X]=9-\dfrac94\pi\approx1.931}$

b. The probability that $X\le3$ is

$P(X\le 3)=\displaystyle\int_{-\infty}^3f_X(x)\,\mathrm dx=\frac29\int_0^3xe^{-x^2/9}\,\mathrm dx$

which can be handled with the same substitution used in part (a). We get

$\boxed{P(X\le 3)=\dfrac{e-1}e\approx0.632}$

c. Same procedure as in (b). We have

$P(1\le X\le3)=P(X\le3)-P(X\le1)$

and

$P(X\le1)=\displaystyle\int_{-\infty}^1f_X(x)\,\mathrm dx=\frac29\int_0^1xe^{-x^2/9}\,\mathrm dx=\frac{e^{1/9}-1}{e^{1/9}}$

Then

$\boxed{P(1\le X\le3)=\dfrac{e^{8/9}-1}e\approx0.527}$

7 0

3 years ago

A lighthouse casts a shadow 32 meters long at the same time a nearby statue casts a shadow that is 9 meters long. If the statue

Pavlova-9 [17]

Answer:

Step-by-step explanation:

Ok, so basically let's start with a proportion.

x/32 = 11.25/9

Cross multiply:

x * 9 = 32 * 11.25

9x = 32 * 11.25

9x = 360

Solving for variable 'x'.

Divide each side by '9'.

x = 40

I don't know if this is the correct answer, but it was based on my math. I hope this helps!

5 0

3 years ago

I'm completely lost?

aliya0001 [1]

13000-5600=7400...that's about it, just multiply then subtract

4 0

3 years ago

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