You measure the lifetime of a random sample of 64 tires of a certain brand. the sample mean is x¯=50 months. suppose that the lifetimes for tires of this brand follow a normal distribution, with unknown mean µ and standard deviation σ=5 months, then a 99% confidence interval for µ is:

(48.3875, 51.6125)

Step-by-step explanation:

At 99% level of significance

From the normal standard deviation table

Considering that

± =50±

50±2.33(0.625)=50±1.6125=(48.3875, 51.6125)

Therefore, there’s 99% confidence that the mean lifetime of a certain brand of tires is between 48.3875 and 51.6125

step-by-step explanation:

answer:

payment just for service  

→

$

87.12

payment for service including tax

→

$

94.09

explanation:

service only with 20% tip  

→

$

72.6

(

1

+

20

100

)

=

$

87.12

in the opening of the question the word 'service' is associated only with the pretax value.

the closing part of the question asks: how much did she pay for the  

service

−−−−−−  

so technically the answer is  

→

$

72.6

(

1

+

20

100

)

=

$

87.12

however, the intention of the question provider may have been that your answer is to be  

$

87.12

(

1

+

8

100

)

=

$

94.09

to 2 decimal places.

'

payment just for service  

→

$

87.12

payment for service including tax

→

$

94.09

tony b

mar 21, 2017

answer:

trying to explain it another way

explanation:

service charge  

.

→

$

72.60

20% tip  

20

100

×

$

72.60

=

$

14.52

−−−−−−  

←

add

$

87.12

tax  

8

100

×

$

87.12

=

$

6.97

−−−−−  

←

add

$

94.09

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