Find m A 10<br> B 15<br> C 30<br> D 60

faltersainse [42]

! is factorial
it means multipliy all numbers from 1 to that number together
example
1!=1
2!=2*1
3!=3*2*1
etc

some things to note
7!*8=8!
4!*5*6=6!

$\frac{(4!)(7!)}{(6!)(8!)}$
so we can rewrite it as
$\frac{(4!)(7!)}{(4!)(5)(6)(7!)(8)}$ =
$\frac{1}{(5)(6)(8)}$ =
$\frac{1}{240}$

4 0

4 years ago

Assume that the helium porosity (in percentage) of coal samples taken from any particular seam is normally distributed with true

Feliz [49]

Answer:

a) The 95% CI for the true average porosity is (4.51, 5.19).

b) The 98% CI for true average porosity is (4.11, 5.01)

c) A sample size of 15 is needed.

d) A sample size of 101 is needed.

Step-by-step explanation:

a. Compute a 95% CI for the true average porosity of a certain seam if the average porosity for 20 specimens from the seam was 4.85.

We have that to find our $\alpha$ level, that is the subtraction of 1 by the confidence interval divided by 2. So:

$\alpha = \frac{1-0.95}{2} = 0.025$

Now, we have to find z in the Ztable as such z has a pvalue of $1-\alpha$ .

So it is z with a pvalue of $1-0.025 = 0.975$ , so $z = 1.96$

Now, find the margin of error M as such

$M = z*\frac{\sigma}{\sqrt{n}}$

In which $\sigma$ is the standard deviation of the population and n is the size of the sample.

$M = 1.96*\frac{0.78}{\sqrt{20}} = 0.34$

The lower end of the interval is the sample mean subtracted by M. So it is 4.85 - 0.34 = 4.51

The upper end of the interval is the sample mean added to M. So it is 4.35 + 0.34 = 5.19

The 95% CI for the true average porosity is (4.51, 5.19).

b. Compute a 98% CI for true average porosity of another seam based on 16 specimens with a sample average of 4.56.

Following the same logic as a.

98% C.I., so $z = 2.327$

$M = 2.327*\frac{0.78}{\sqrt{16}} = 0.45$

4.56 - 0.45 = 4.11

4.56 + 0.45 = 5.01

The 98% CI for true average porosity is (4.11, 5.01)

c. How large a sample size is necessary if the width of the 95% interval is to be 0.40?

A sample size of n is needed.

n is found when M = 0.4.

95% C.I., so Z = 1.96.

$M = z*\frac{\sigma}{\sqrt{n}}$

$0.4 = 1.96*\frac{0.78}{\sqrt{n}}$

$0.4\sqrt{n} = 1.96*0.78$

$\sqrt{n} = \frac{1.96*0.78}{0.4}$

$(\sqrt{n})^{2} = (\frac{1.96*0.78}{0.4})^{2}$

$n = 14.6$

Rounding up

A sample size of 15 is needed.

d. What sample size is necessary to estimate the true average porosity to within 0.2 with 99% confidence?

99% C.I., so z = 2.575

n when M = 0.2.

$M = z*\frac{\sigma}{\sqrt{n}}$

$0.2 = 2.575*\frac{0.78}{\sqrt{n}}$

$0.2\sqrt{n} = 2.575*0.78$

$\sqrt{n} = \frac{2.575*0.78}{0.2}$

$(\sqrt{n})^{2} = (\frac{2.575*0.78}{0.2})^{2}$

$n = 100.85$

Rounding up

A sample size of 101 is needed.

8 0

3 years ago

An eight character password uses four digits 1-6 and four letters A-Z with repeats allowed. How many possible passwords like thi

Ratling [72]

4 x 8 x 6 x 4 x 26 = 19,968

i think however, i could be wrong. my teacher told me to use the fundamental counting principle. you multiply each different part of the problem.

3 0

4 years ago

Please help me with this. Attention all smart people!!!

olya-2409 [2.1K]

Answer: CPCTC

Step-by-step explanation:

because in the step before that it was proved that the triangles were congruent and CPCTC is used after they are proved congruent.

By CPCT [Corresponding Part of congruent Triangle]

<h=<j

hope i helped

-lvr

5 0

3 years ago

Brad jumps 4 feet forward and then 2 feet backward.How many full sets must he jump to each 16 feet

julsineya [31]

8 sets, she’s only traveling 2 feet forward per each set 2*x=16 x=8

6 0

2 years ago

Find m A 10 B 15 C 30 D 60