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1 year ago

Solve: log8 (x - 4) = 2

Mathematics

2 answers:

Black_prince [1.1K]1 year ago

7 0

Answer:

x = 68

Step-by-step explanation:

Given equation:

$\rm log_{8}(x - 4) = 2$

To Find:

Value of x

Solution:

Rewrite the equation in exponential form which is equivalent to b^y = x.

$\implies {8}^{2} = x - 4$

Now find the value of x.

$\implies \:64 = x - 4$

Transpose 4 from RHS to LHS, make sure to change its sign from (-) to (+) .

$\implies \: 64 + 4 = x$

Overturn the equation

$\implies \: x = 68$

Thus, value of x is 68.

Vsevolod [243]1 year ago

4 0

Answer:

x = 68

Explanation:

⇒ log₈(x - 4) = 2

apply log rules: logₐN = x then N = aˣ

⇒ (x - 4) = 8²

simplify

⇒ x - 4 = 64

add 4 on both sides

⇒ x = 64 + 4

add the integers

⇒ x = 68

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Answer:

a) $P(X$

And we can find this probability using the normal standard distribution or excel and we got:

$P(z$

b) $P(X>40)=P(\frac{X-\mu}{\sigma}>\frac{60-\mu}{\sigma})=P(Z>\frac{60-43}{4.5})=P(z>3.78)$

And we can find this probability using the complement rule and normal standard distribution or excel and we got:

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c) $z=0.674$

And if we solve for a we got

$a=43 +0.674*4.5=46.033$

So the value of height that separates the bottom 75% of data from the top 25% is 46.033.

Step-by-step explanation:

Previous concepts

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".

The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".

Solution to the problem

Let X the random variable that represent the heights of a population, and for this case we know the distribution for X is given by:

$X \sim N(43,4.5)$

Where $\mu=43$ and $\sigma=4.5$

Part a

We are interested on this probability

$P(X$

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

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

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

$P(X$

And we can find this probability using the normal standard distribution or excel and we got:

$P(z$

Part b

$P(X>40)=P(\frac{X-\mu}{\sigma}>\frac{60-\mu}{\sigma})=P(Z>\frac{60-43}{4.5})=P(z>3.78)$

And we can find this probability using the complement rule and normal standard distribution or excel and we got:

$P(z>3.78)=1-P(Z$

Part c

For this part we want to find a value a, such that we satisfy this condition:

$P(X>a)=0.25$ (a)

$P(X$ (b)

Both conditions are equivalent on this case. We can use the z score again in order to find the value a.

As we can see on the figure attached the z value that satisfy the condition with 0.75 of the area on the left and 0.25 of the area on the right it's z=0.674. On this case P(Z<0.674)=0.75 and P(z>0.674)=0.25

If we use condition (b) from previous we have this:

$P(X$

$P(z$

But we know which value of z satisfy the previous equation so then we can do this:

$z=0.674$

And if we solve for a we got

$a=43 +0.674*4.5=46.033$

So the value of height that separates the bottom 75% of data from the top 25% is 46.033.

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