Mathematics, 24.03.2020 17:59, ajadegipson6784

One step in the manufacture of a certain metal clamp involves the drilling of four holes. In a sample of 150 clamps, the average time needed to complete this step was 72 seconds and the standard deviation was 10 seconds. (a) Find an 87% confidence interval for the mean time needed to complete the step. (b) What is the confidence level of the interval (69, 75)

Answers: 2

Show answers

Answers

answered: Joshuafranklindude

a) $72-1.52\frac{10}{\sqrt{150}}=70.76$

$72+1.52\frac{10}{\sqrt{150}}=73.24$

So on this case the 87% confidence interval would be given by (70.76;73.24)

b) $ME= \frac{75-69}{2}= 3$

And the margin of error is given by:

$ME=t_{\alpha/2}\frac{s}{\sqrt{n}}$

And replacing we can solve for the critical value $t_{\alpha/2}$

And we got:

$t_{\alpha/2}= \frac{ME*\sqrt{n}}{s}= \frac{3* \sqrt{150}}{10}= 3.674$

And we can find the significance level with this formula:

"=2*T.DIST(-3.674;149;TRUE)"

And the confidence level would be 1-0.000332= 0.999668

And then that correspond to 99.96%

Step-by-step explanation:

Previous concepts

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The margin of error is the range of values below and above the sample statistic in a confidence interval.

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".

$\bar X=72$ represent the sample mean

$\mu$ population mean (variable of interest)

s=10 represent the sample standard deviation

n=150 represent the sample size

87% confidence interval

Part a

The confidence interval for the mean is given by the following formula:

$\bar X \pm t_{\alpha/2}\frac{s}{\sqrt{n}}$ (1)

The degrees of freedom are given by:

df = 150-1=149

Since the Confidence is 0.87 or 87%, the value of $\alpha=0.13$ and $\alpha/2 =0.065$ , and we can use excel, a calculator or a tabel to find the critical value. The excel command would be: "=-T.INV(0.065,149)".And we see that $z_{\alpha/2}=1.52$

Now we have everything in order to replace into formula (1):

$72-1.52\frac{10}{\sqrt{150}}=70.76$

$72+1.52\frac{10}{\sqrt{150}}=73.24$

So on this case the 87% confidence interval would be given by (70.76;73.24)

Part b

For this case the confidence interval is given by: (69,75)

We can estimate the margin of error like this:

$ME= \frac{75-69}{2}= 3$

And the margin of error is given by:

$ME=t_{\alpha/2}\frac{s}{\sqrt{n}}$

And replacing we can solve for the critical value $t_{\alpha/2}$

And we got:

$t_{\alpha/2}= \frac{ME*\sqrt{n}}{s}= \frac{3* \sqrt{150}}{10}= 3.674$

And we can find the significance level with this formula:

"=2*T.DIST(-3.674;149;TRUE)"

And the confidence level would be 1-0.000332= 0.999668

And then that correspond to 99.96%

answered: Guest

step-by-step explanation:

answered: Guest

6.5

step-by-step explanation:

you said it was in the question

~courtney

Other questions on the subject: Mathematics

Mathematics, 21.06.2019 17:30, nae9587

Arefrigeration system at your company uses temperature sensors fixed to read celsius (°c) values, but the system operators in your control room understand only the fahrenheit scale. you have been asked to make a fahrenheit (°f) label for the high temperature alarm, which is set to ring whenever the system temperature rises above –10°c. what fahrenheit value should you write on the label

Answers: 1

continue

Mathematics, 21.06.2019 18:00, reinaelane77

Ling listed all of the factors of a mystery number: 1,2,4,8,16,32 what is the mystery number?

Answers: 2

continue

Mathematics, 21.06.2019 21:00, rpmgamer

Seattle, washington is known for being rainy. one day last month, 8 inches of rain fell in 1 1/2 hours. what us the rate of the rainfall expressed in ft per plzzz write a proportion i will give you 100 points

Answers: 1

continue

Mathematics, 21.06.2019 23:30, drakkeo

Sam opened a money-market account that pays 3% simple interest. he started the account with $7,000 and made no further deposits. when he closed the account, he had earned $420 in interest. how long did he keep his account open?

Answers: 1

continue

Do you know the correct answer?

One step in the manufacture of a certain metal clamp involves the drilling of four holes. In a sampl...