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leonid [27]
3 years ago
9

There is a sales tax of $20 on an item that costs $128 before tax. The sales tax on a second item is $6.75 . How much does the s

econd item cost before tax?
Mathematics
1 answer:
Kazeer [188]3 years ago
8 0

$20/128 = 6.75/x

using cross products

20x=128*6.75

divide by 20

x =43.20

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The mean waiting time at the drive-through of a fast-food restaurant from the time the food is ordered to when it is received is
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Answer:

a) And if we replace we got: \bar X= 78

s = 15.391

b) 78-3.25\frac{15.391}{\sqrt{10}}=62.182    

78-3.25\frac{15.391}{\sqrt{10}}=93.818    

So on this case the 99% confidence interval would be given by (62.182;93.818)    

Step-by-step explanation:

Dataset given: 109 67 58 76 65 80 96 86 71 72

Part a

For this case we can calculate the sample mean with the following formula:

\bar X = \frac{\sum_{i=1}^n X_i}{n}

And if we replace we got: \bar X= 78

And the deviation is given by:

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And if we replace we got s = 15.391

Part b

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

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

In order to calculate the critical value t_{\alpha/2} we need to find first the degrees of freedom, given by:

df=n-1=10-1=9

Since the Confidence is 0.99 or 99%, the value of \alpha=0.01 and \alpha/2 =0.005, and we can use excel, a calculator or a table to find the critical value. The excel command would be: "=-T.INV(0.005,9)".And we see that t_{\alpha/2}=3.25

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

78-3.25\frac{15.391}{\sqrt{10}}=62.182    

78-3.25\frac{15.391}{\sqrt{10}}=93.818    

So on this case the 99% confidence interval would be given by (62.182;93.818)    

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