1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
VMariaS [17]
3 years ago
10

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

standard deviation 0.75. (a) compute a 95% ci for the true average porosity of a certain seam if the average porosity for 25 specimens from the seam was 4.85. (round your answers to two decimal places.) , (b) compute a 98% ci for true average porosity of another seam based on 15 specimens with a sample average porosity of 4.56. (round your answers to two decimal places.) , (c) how large a sample size is necessary if the width
Mathematics
1 answer:
aev [14]3 years ago
7 0
A) 4.85\pm0.29
B) 4.56\pm0.45

We first find the z-score associated with the level of confidence.  For 95% confidence:
Convert 95% to a decimal:  0.95
Subtract from 1:  1-0.95 = 0.05
Divide by 2 (this is the area in the tails):  0.05/2 = 0.025
Subtract from 1 (we don't want the tails, we want the area in the middle):  1-0.025 = 0.975

Using a z-table (http://www.z-table.com) we find the z-score for this is 1.96.  We now use the formula
\overline{x} \pm z*(\frac{\sigma}{\sqrt{n}})
=4.85\pm 1.96*(\frac{0.75}{\sqrt{25}})=4.85\pm0.294\approx 4.85\pm 0.29

For a 98% confidence level:
Convert 98% to a decimal:  0.98
Subtract from 1:  1 - 0.98 = 0.02
Divide by 2:  0.02/2 = 0.01
Subtract from 1:  1 - 0.01 = 0.99

Using the z-table we see the closest number to this is for the z-score 2.33:
\overline{x} \pm z* (\frac{\sigma}{\sqrt{n}})
=4.56\pm 2.33*(\frac{0.75}{\sqrt{15}})=4.56\pm0.45
You might be interested in
The volume of a cone is 16x cubic inches, Its height is 12 inches. What is the radius of the cone?
Dimas [21]
The radius would be 2
4 0
3 years ago
P(x)=×^4-x^2-3<br>use the remainder theorem and synthetic division to find p(-2)
xxTIMURxx [149]

Answer: p(-2)=9


Step-by-step explanation:


8 0
3 years ago
1 2/3. 7/8 someone help me please
Ksivusya [100]
1 2/3 * 7/8...turn the mixed number to an improper fraction
5/3 * 7/8 = 35/24 = 1 11/24
3 0
3 years ago
Read 2 more answers
X+3menor que 8 qual o resultado
elixir [45]

x+3<8

8-3 =5

 X<5

 any number less than 5 will work

7 0
3 years ago
A 75-gallon tank is filled with brine (water nearly saturated with salt; used as a preservative) holding 11 pounds of salt in so
Debora [2.8K]

Let A(t) = amount of salt (in pounds) in the tank at time t (in minutes). Then A(0) = 11.

Salt flows in at a rate

\left(0.6\dfrac{\rm lb}{\rm gal}\right) \left(3\dfrac{\rm gal}{\rm min}\right) = \dfrac95 \dfrac{\rm lb}{\rm min}

and flows out at a rate

\left(\dfrac{A(t)\,\rm lb}{75\,\rm gal + \left(3\frac{\rm gal}{\rm min} - 3.25\frac{\rm gal}{\rm min}\right)t}\right) \left(3.25\dfrac{\rm gal}{\rm min}\right) = \dfrac{13A(t)}{300-t} \dfrac{\rm lb}{\rm min}

where 4 quarts = 1 gallon so 13 quarts = 3.25 gallon.

Then the net rate of salt flow is given by the differential equation

\dfrac{dA}{dt} = \dfrac95 - \dfrac{13A}{300-t}

which I'll solve with the integrating factor method.

\dfrac{dA}{dt} + \dfrac{13}{300-t} A = \dfrac95

-\dfrac1{(300-t)^{13}} \dfrac{dA}{dt} - \dfrac{13}{(300-t)^{14}} A = -\dfrac9{5(300-t)^{13}}

\dfrac d{dt} \left(-\dfrac1{(300-t)^{13}} A\right) = -\dfrac9{5(300-t)^{13}}

Integrate both sides. By the fundamental theorem of calculus,

\displaystyle -\dfrac1{(300-t)^{13}} A = -\dfrac1{(300-t)^{13}} A\bigg|_{t=0} - \frac95 \int_0^t \frac{du}{(300-u)^{13}}

\displaystyle -\dfrac1{(300-t)^{13}} A = -\dfrac{11}{300^{13}} - \frac95 \times \dfrac1{12} \left(\frac1{(300-t)^{12}} - \frac1{300^{12}}\right)

\displaystyle -\dfrac1{(300-t)^{13}} A = \dfrac{34}{300^{13}} - \frac3{20}\frac1{(300-t)^{12}}

\displaystyle A = \frac3{20} (300-t) - \dfrac{34}{300^{13}}(300-t)^{13}

\displaystyle A = 45 \left(1 - \frac t{300}\right) - 34 \left(1 - \frac t{300}\right)^{13}

After 1 hour = 60 minutes, the tank will contain

A(60) = 45 \left(1 - \dfrac {60}{300}\right) - 34 \left(1 - \dfrac {60}{300}\right)^{13} = 45\left(\dfrac45\right) - 34 \left(\dfrac45\right)^{13} \approx 34.131

pounds of salt.

7 0
1 year ago
Other questions:
  • Miss white wants to buy 5 value meals at mel's diner.What is a resonable total for her purchase
    11·2 answers
  • NEED HELP FAST WILL GIVE BRAILYIST What is the solution to Negative 1 minus 7?<br><br> –8 –6 6 8
    10·1 answer
  • Please answer this multiple choice question!! will give brainliest :)
    12·1 answer
  • G use part 1 of the fundamental theorem of calculus to find the derivative of the function. sqrt(4+7t)
    8·1 answer
  • Uh need a bit of help with this question
    9·2 answers
  • Shia received a large package in the mail. What is a reasonable weight for the large package? A 20 grams B 36 pounds C 52 ML D 6
    12·1 answer
  • How many units is -9 from zero on the number line?
    13·2 answers
  • How do you divide 54,164 by 44 and show your work
    10·1 answer
  • Evaluate<br>x+y+z when x=3, y=2 ,z=1​
    15·1 answer
  • Help pls Ill mark brainliest
    6·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!