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3 years ago

What is the standard deviation of a normal distribution, whose mean is 35, in which an x-value of 23 has a z-score of -1.63?

Mathematics

1 answer:

Dvinal [7]3 years ago

6 0

Answer:

7.36

Step-by-step explanation:

z-score is:

z = (x − μ) / σ

Given that z = -1.63, x = 23, and μ = 35:

-1.63 = (23 − 35) / σ

σ ≈ 7.36

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Setler [38]

The length of all the sides is same, if u want to write it as an expression, you can write it as any variable, x,y or z

6 0

2 years ago

Let X ~ N(0, 1) and Y = eX. Y is called a log-normal random variable.

Cloud [144]

If $F_Y(y)$ is the cumulative distribution function for $Y$ , then

$F_Y(y)=P(Y\le y)=P(e^X\le y)=P(X\le\ln y)=F_X(\ln y)$

Then the probability density function for $Y$ is $f_Y(y)={F_Y}'(y)$ :

$f_Y(y)=\dfrac{\mathrm d}{\mathrm dy}F_X(\ln y)=\dfrac1yf_X(\ln y)=\begin{cases}\frac1{y\sqrt{2\pi}}e^{-\frac12(\ln y)^2}&\text{for }y>0\\0&\text{otherwise}\end{cases}$

The $n$ th moment of $Y$ is

$E[Y^n]=\displaystyle\int_{-\infty}^\infty y^nf_Y(y)\,\mathrm dy=\frac1{\sqrt{2\pi}}\int_0^\infty y^{n-1}e^{-\frac12(\ln y)^2}\,\mathrm dy$

Let $u=\ln y$ , so that $\mathrm du=\frac{\mathrm dy}y$ and $y^n=e^{nu}$ :

$E[Y^n]=\displaystyle\frac1{\sqrt{2\pi}}\int_{-\infty}^\infty e^{nu}e^{-\frac12u^2}\,\mathrm du=\frac1{\sqrt{2\pi}}\int_{-\infty}^\infty e^{nu-\frac12u^2}\,\mathrm du$

Complete the square in the exponent:

$nu-\dfrac12u^2=-\dfrac12(u^2-2nu+n^2-n^2)=\dfrac12n^2-\dfrac12(u-n)^2$

$E[Y^n]=\displaystyle\frac1{\sqrt{2\pi}}\int_{-\infty}^\infty e^{\frac12(n^2-(u-n)^2)}\,\mathrm du=\frac{e^{\frac12n^2}}{\sqrt{2\pi}}\int_{-\infty}^\infty e^{-\frac12(u-n)^2}\,\mathrm du$

But $\frac1{\sqrt{2\pi}}e^{-\frac12(u-n)^2}$ is exactly the PDF of a normal distribution with mean $n$ and variance 1; in other words, the 0th moment of a random variable $U\sim N(n,1)$ :

$E[U^0]=\displaystyle\frac1{\sqrt{2\pi}}\int_{-\infty}^\infty e^{-\frac12(u-n)^2}\,\mathrm du=1$

so we end up with

$E[Y^n]=e^{\frac12n^2}$

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2 years ago

Pyramids and cones have how many base

Blababa [14]

Answer:

pyramids and cones have 1 base.

Step-by-step explanation:

4 0

2 years ago

What is the approximate value of irrational number e (round to 5 decimal places)?

saveliy_v [14]

Answer:

2.71828

Step-by-step explanation:

took the quiz and got it right

6 0

3 years ago

I need only 16 and 17 please help

Nesterboy [21]

9514 1404 393

Answer:

16. a: (-90°, (4, 3)); b: (90°, (0, 3)); c: (-90°, (0, 0))

17. a: (down, (4, -1)); b: (right, (4, 3)); c: (up, (5, 2))

Step-by-step explanation:

We don't know what notation you're used to seeing for rotations. Here. we'll use the form [degrees CCW, (center)]. (CW angles are negative.) In any rotation, the center is the point that is invariant (remains in the same place)

16.

a) The tail is invariant, so the rotation is (-90°, (4, 3)).

b) The tip is invariant, so the rotation is (90°, (0, 3)).

c) The origin is invariant, so the rotation is (-90°, (0, 0))

17.

a) The tail is invariant, so the arrow is pointing down with the tip at (4, -1).

b) The center is invariant, so the arrow is reversed. It is pointing right with the tip at (4, 3).

c) Point (2, 3) is invariant, so the arrow is pointing up with the center at (5, 0). The tip is at (5, 2).

_____

<em>Additional comment</em>

If you have trouble visualizing these rotations, you might find it useful to trace the arrow on a piece of (semi-)transparent medium (plastic or tracing paper) so that you can move it as required to match the descriptions in the problem statement. A pin, or a dot on your tracing, can serve to fix the center of rotation. A little hands-on never hurts in math and geometry.

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3 years ago