In order to estimate the average electric usage per month, a sample of 81 houses was selected and the electric usage was determined. Assume a population standard deviation of 450 kilowatt-hours. If the sample mean is 1858 kWh, the 95% confidence interval estimate of the population mean is _________?

Answers

Answer 1
Answer:

Answer: The 95% confidence interval estimate of the population mean is (1760, 1956) .

Step-by-step explanation:

Formula for confidence interval for population mean((\mu)) :

\overline{x}\pm z^*(\sigma)/(√(n))

, where n= Sample size

\overline{x} = sample mean.

z^* = Two-tailed critical z-value

\sigma = population standard deviation.

By considering the given information, we have

n= 81

\sigma=450 kilowatt-hours.

\overline{x}=1858 kilowatt-hours.

By using the z-value table ,

The critical values for 95% confidence interval : z^*=\pm1.960

Now , the 95% confidence interval estimate of the population mean will be :

1858\pm (1.960)(450)/(√(81))\n\n=1858\pm(1.960)(450)/(9)=1858\pm98\n\n=(1858-98,\ 1858+98)\n\n=(1760,\ 1956)

Hence, the 95% confidence interval estimate of the population mean is (1760, 1956) .


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A certain vibrating system satisfies the equation u'' + γu' + u = 0. Find the value of the damping coefficient γ for which the quasi period of the damped motion is 90% greater than the period of the corresponding undamped motion.

Answers

Final answer:

In damped harmonic motion, we calculate damping coefficient γ by comparing the periods of damped and undamped motion. For the given situation where the quasi-period is 90% greater than the undamped period, the damping coefficient is approximately 0.7416.

Explanation:

The subject of this question involves Damped Harmonic Motion, a concept in Physics, related to vibrations and waves. The equation given, u'' + γu' + u = 0, describes the motion where γ denotes the damping coefficient. Here, we have to calculate this damping coefficient when the quasi period of the damped motion is 90% greater than the period of the corresponding undamped motion.

To solve this, we must use the relationship between damped and undamped periods. The quasi-period T' of a damped harmonic motion relates to the undamped period T as: T' = T/(sqrt(1 - (γ/2)^2)). Now, given that T' = 1.9T, we can but these two equations together:

1.9 = 1/(sqrt(1 - (γ/2)^2))

Solving this for γ, we get γ ≈ 0.7416. Hence, the damping coefficient γ for which the quasi period of the damped motion is 90% greater than the period of the corresponding undamped motion is approximately 0.7416.

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Final answer:

The value of the damping coefficient γ for which the quasi period of the damped motion is 90% greater than the period of the undamped motion is the one that satisfies γ=2*ω*0.9, where ω is the natural frequency of oscillation.

Explanation:

The given equation is for a damped harmonic oscillator, a physical system that oscillates under both a restoring force and a damping force proportional to the velocity of the system. The damping coefficient γ determines the behavior of the system and in this case, we need to find the value of γ such that the quasi period of the damped motion is 90% greater than the period of the undamped motion.

The period of the undamped motion, T₀, is calculated by the formula T₀=2π/sqrt(ω), where ω is the natural frequency of oscillation. The quasi period of the damped motion, Td, is increased by a factor of 1+η (in this case, 1.9 as the increase is 90%) and calculated by the formula Td=T₀(1+η) = T₀*1.9.

The damping ratio η is determined by the damping coefficient γ as η=γ/2ω. Therefore, by combining these expressions and rearranging the terms, we extract γ from these formulas as γ=2ω*η => γ=2*ω*(0.9). Thus, the value of the damping coefficient γ for which the quasi period of the damped motion is 90% greater than the period of the corresponding undamped motion is the one which satisfies γ=2*ω*0.9.

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Look at this cube, please help

Answers

Let's find the current surface area of the cube.

A = 6a^2

A = 6

Now let's find the surface area of the cube when tripled.

A = 6(3^2)

A = 54

54/6 = 9

So, the answer should be the new surface area will be 9 times the old surface area.

Answer:the new surface will be 9 times the old surface area

Step-by-step explanation:

Suppose that there are 27 sophomores and 14 juniors in a Physiology class. Two students are chosen at random to participate in a class demonstration. What is theprobability of choosing two students at random and the first is a junior and the second one is a sophomore? Round your answer to four decimal places, if necessary.

Answers

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Step-by-step explanation:

Which is the equation of a line that has a slope of -3 and passes through point
(-3,-1)

Answers

Answer:

Use y-y1 = m*(x-x1) where m = slope and (x1,y1) is the point.

Step-by-step explanation:

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In the problem 14 = 2 = 7, which number is the divisor?

Answers

Answer:

14 and 7 or 14 and 2

Step-by-step explanation:

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Answer:

2, assuming you meant 14÷2=7

Step-by-step explanation: