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2 years ago

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The electric cooperative needs to know the mean household usage of electricity by its non-commercial customers in kWh per day. T

hey would like the estimate to have a maximum error of 0.15 kWh. A previous study found that for an average family the standard deviation is 1.9 kWh and the mean is 16.7 kWh per day. If they are using a 98% level of confidence, how large of a sample is required to estimate the mean usage of electricity? Round your answer up to the next integer

1 answer:

Bogdan [553]2 years ago

7 0

Answer: 263

Step-by-step explanation:

As per given , we have

Population standard deviation : $\sigma=1.9\text{ kWh}$

maximum error : E=0.15 kWh

Significance level : $\alpha=1-0.98=0.02$

Critical value for 98% confidence interval : $z_{\alpha/2}=1.28$

Formula to find the sample size :

$n=(\dfrac{z_{\alpha/2}\cdot \sigma}{E})^2\\\\=(\dfrac{1.28\times1.9}{0.15})^2\\\\=262.872177778\approx263$

Hence, the minimum sample size required =263

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Determine if each of the following sets is a subspace of ℙn, for an appropriate value of n. Type "yes" or "no" for each answer.

xxMikexx [17]

Answer:

1. Yes.

2. No.

3. Yes.

Step-by-step explanation:

Consider the following subsets of Pn given by

1.Let W1 be the set of all polynomials of the form $p(t)=at^2$ , where a is in ℝ.

2.Let W2 be the set of all polynomials of the form $p(t)=t^2+a$ , where a is in ℝ.

3. Let W3 be the set of all polynomials of the form $p(t)=at^2+at$ , where a is in ℝ.

Recall that given a vector space V, a subset W of V is a subspace if the following criteria hold:

- The 0 vector of V is in W.

- Given v,w in W then v+w is in W.

- Given v in W and a a real number, then av is in W.

So, for us to check if the three subsets are a subset of Pn, we must check the three criteria.

- First property:

Note that for W2, for any value of a, the polynomial we get is not the zero polynomial. Hence the first criteria is not met. Then, W2 is not a subspace of Pn.

For W1 and W3, note that if a= 0, then we have p(t) =0, so the zero polynomial is in W1 and W3.

- Second property:

W1. Consider two elements in W1, say, consider a,b different non-zero real numbers and consider the polynomials

$p_1 (t) = at^2, p_2(t)=bt^2$ .

We must check that p_1+p_2(t) is in W1.

Note that

$p_1(t)+p_2(t) = at^2+bt^2 = (a+b)t^2$

Since a+b is another real number, we have that p1(t)+p2(t) is in W1.

W3. Consider two elements in W3. Say $p_1(t) = a(t^2+t), p_2(t)= b(t^2+t)$ . Then

$p_1(t) + p_2(t) = a(t^2+t) + b(t^2+t) = (a+b) (t^2+t)$

So, again, p1(t)+p2(t) is in W3.

- Third property.

W1. Consider an element in W1 $p(t) = at^2$ and a real scalar b. Then

$bp(t) = b(at^2) = (ba)t^2)$ .

Since (ba) is another real scalar, we have that bp(t) is in W1.

W3. Consider an element in W3 $p(t) = a(t^2+t)$ and a real scalar b. Then

$bp(t) = b(a(t^2+t)) = (ba)(t^2+t)$ .

Since (ba) is another real scalar, we have that bp(t) is in W3.

After all,

W1 and W3 are subspaces of Pn for n= 2

and W2 is not a subspace of Pn.

6 0

2 years ago

The caller times at a customer service center has an exponential distribution with an average of 22 seconds. Find the probabilit

jenyasd209 [6]

Answer:

The probability that a randomly selected call time will be less than 30 seconds is 0.7443.

Step-by-step explanation:

We are given that the caller times at a customer service center has an exponential distribution with an average of 22 seconds.

Let X = caller times at a customer service center

The probability distribution (pdf) of the exponential distribution is given by;

$f(x) = \lambda e^{-\lambda x} ; x > 0$

Here, $\lambda$ = exponential parameter

Now, the mean of the exponential distribution is given by;

Mean = $\frac{1}{\lambda}$

So, $22=\frac{1}{\lambda}$ ⇒ $\lambda=\frac{1}{22}$

SO, X ~ Exp( $\lambda=\frac{1}{22}$ )

To find the given probability we will use cumulative distribution function (cdf) of the exponential distribution, i.e;

$P(X\leq x) = 1 - e^{-\lambda x}$ ; x > 0

Now, the probability that a randomly selected call time will be less than 30 seconds is given by = P(X < 30 seconds)

P(X < 30) = $1 - e^{-\frac{1}{22} \times 30}$

= 1 - 0.2557

= 0.7443

7 0

2 years ago

In how many ways can you spell the word ROOM in the grid below? You can start on any letter R, then on each step you can step on

Zina [86]

Answer:

84? Not sure but pretty sure

Step-by-step explanation:

In a straight line, the word can only be spelled on the diagonals, and there are only two diagonals in each direction that have 2 O's.

If 90° and reflex turns are allowed, then the number substantially increases.

Corner R: can only go to the adjacent diagonal O, and from there to one other O, then to any of the 3 M's, for a total of 3 paths.

2nd R from the left: can go to either of two O's, one of which is the same corner O as above. So it has the same 3 paths. The center O can go to any of 4 Os that are adjacent to an M, for a total of 10 more paths. That's 13 paths from the 2nd R.

Middle R can go the three O's on the adjacent row, so can access the three paths available from each corner O along with the 10 paths available from the center O, for a total of 16 paths.

Then paths accessible from the top row of R's are 3 +10 +16 +10 +3 = 42 paths. There are two such rows of R's so a total of 84 paths.

6 0

1 year ago

Read 2 more answers

Greenfields is a mail order seed and plant business. The size of orders is uniformly distributed over the interval from $25 to $

LekaFEV [45]

Answer:

a) 47.55

b) 58

c) 47.88

Step-by-step explanation:

Given that the size of the orders is uniformly distributed over the interval

$25 ( a ) to $80 ( b )

<u>a) Determine the value for the first order size generated based on 0.41</u>

parameter for normal distribution is given as ; a = 25, b = 80

size/value of order = a + random number ( b - a )

= 25 + 0.41 ( 80 - 25 )

= 47.55

<u>b) Value of the last order generated based on random number (0.6)</u>

= a + random number ( b - a )

= 25 + 0.6 ( 80 - 25 )

= 25 + 33 = 58

<u>c) Average order size </u>

= ∑ order 1 + order 2 + ----- + order 10 ) / 10

= (47.55 + ...... + 58 ) / 10

= 478.8 / 10 = 47.88

4 0

2 years ago

A 3 kg toy car rests st the top of a 0.45 meter ramp. What is its gravitational potential energy?

salantis [7]

<span>gravitational potential energy : P
Gravity : g
Mass : m
height : h

P = mgh = 3 x 9.8 x 0.45 = 13.23 Joule

Potential energy is work , from the known formula

W = Fd ( work = force x distance )

W = P ( in case of potential energy height change)

F is the force acting on the body in case of ideal ramp , the only force acting is the weight of the body

F = mg ( not just <m> as the force is mg (Newton) gravity effect)

d is the displacement in direction of force, as we have considered the force to be the weight not it's component in direction of the ramp , the change in displacement is the change in height so

d = h

W = Fd = (F = mg) x (d = h) = mgh

W = mgh = P

</span>

7 0

2 years ago