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qwelly [4]
3 years ago
15

An auto mechanic knows the average time it takes to replace a defective car radiator is 70 minutes with a standard deviation of

12 minutes. this average is based on a random sample of 50. which excel statements will construct a 90% confidence interval for the time needed to replace a defective car radiator?
a. =70+1.96*12/sqrt(50), and =70-1.96*12/sqrt(50)
b. =70+1.96*3.46/sqrt(50), and =70-1.96*3.46/sqrt(50)
c. =70+1.645*3.46/sqrt(50), and =70-1.645*3.46/sqrt(50)
d. =70+1.645*12/sqrt(50), and =70-1.645*12/sqrt(50)
e. none of the above.
Mathematics
1 answer:
horsena [70]3 years ago
8 0
<span>Given that the average time it takes to replace a defective car radiator is 70 minutes with a standard deviation of 12 minutes.

The 90% confidence interval of a random sample of 50 is given by

90\% \ C.I.=70\pm1.645 \frac{12}{\sqrt{50}}  \\  \\ \Rightarrow 70+1.645 \frac{12}{\sqrt{50}} \ and \ 70-1.645 \frac{12}{\sqrt{50}}</span>
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Consider the vectors a =3i +j −k, b =i +j +4k, c=i +3j +k, d =−i −3j +k, g =−3i −j +k. Which pairs (if any) of these vectors are
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a and b are perpendicular to each other, as are b and d, b and g

Step-by-step explanation:

To check whether two vectors are perpendicular to each other, we need the angle between these vectors to be 90 degrees.

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The cosine of the angle \theta between two vectors is equal to the dot product of this vectors divided by the product of vector magnitude.

So

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Now, for your exercise, let's compute the dot product between these vectors.

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a.b = (3,1,-1).(1,1,4) = 3+1-4 = 0

So a and b are perpendicular to each other.

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a.c = (3,1,-1).(1,3,1) = 3+3-1 = 5

a and c are not perpendicular to each other.

--------------

a.d = (3,1,-1).(-1,-3,1) = -3-3-1 = -7

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a.g = (3,1,-1).(-3,-1,1) = -9-1-1 = -11

Not

-----------------

b.c = (1,1,4).(1,3,1) = 1+3+4 = 8

Not

------------------

b.d = (1,1,4).(-1,-3,1) = -1 -3 +4 = 0

b.d = 0, so b and d are perpendicular to each other

--------------------

b.g = (1,1,4).(-3,-1,1) = -3-1+4 = 0

b.g = 0, perpendicular

---------------------

c.d = (1,3,1).(-1,-3,1) = -1-9+1 = -9

No

-----------------------

c.g = (1,3,1).(-3,-1,1) = -3-3+1 = -5

No

------------------------

d.g = (-1,-3,1).(-3,-1,1) = 3+3+1 = 7

No

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