(b) Use rules of variance to obtain an expression for the variance and standard deviation (standard error) of the estimator in part (a). v(x)=√(x+vn - 0x² +0,² Identify the next step in this rule from the options below. x-5-₂²_0₂² ₁ 2 VX-1 + 2 0₂ OV--1+%2 n1 na OV--1-%2 n1 2 Since standard deviation is the square root of variance, it follows that 01 √22-9/322 n₁ 0,² 0,² 01+02 Ox-√₂ Compute the estimated standard error (in MPa). (Round your answer to three decimal places.) MPa (c) Calculate a point estimate of the ratio a/a₂ of the two standard deviations. (Round your answer to three decimal places.) 4 (d) Suppose a single beam and a single cylinder are randomly selected. Calculate a point estimate (in MPa) of the variance of the difference X - Y between beam strength and cylinder strength. (Round your answer to two decimal places.) MPa2

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Can u help find the answer for b and explain d?
The image contains a detailed explanation and steps for deriving an expression for the variance and standard deviation of an estimator, using variance rules.

---

**(b) Use rules of variance to obtain an expression for the variance and standard deviation (standard error) of the estimator in part (a):**

\[ V(\overline{X} - \overline{Y}) = V(\overline{X}) + V(\overline{Y}) = \frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2} \]

Identify the next step in this rule from the options below:

- \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1^2} + \frac{\sigma_2^2}{n_2^2} \]
- \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1^2} + \frac{\sigma_2^2}{n_2} \]
- \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2} \]  (Selected option)
- \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2^2} \]

Since standard deviation is the square root of variance, it follows that:

\[ \sigma_{\overline{X} - \overline{Y}} = \sqrt{V(\overline{X} - \overline{Y})} \]

Options for the expression:

- \[ \sigma_{\overline{X} - \overline{Y}} = \sqrt{\frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2}} \]
- \[ \sigma_{\overline{X} - \overline{Y}} = \sqrt{\frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2}^2} \]
- \[ \sigma_{\overline{
Transcribed Image Text:The image contains a detailed explanation and steps for deriving an expression for the variance and standard deviation of an estimator, using variance rules. --- **(b) Use rules of variance to obtain an expression for the variance and standard deviation (standard error) of the estimator in part (a):** \[ V(\overline{X} - \overline{Y}) = V(\overline{X}) + V(\overline{Y}) = \frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2} \] Identify the next step in this rule from the options below: - \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1^2} + \frac{\sigma_2^2}{n_2^2} \] - \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1^2} + \frac{\sigma_2^2}{n_2} \] - \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2} \] (Selected option) - \[ V(\overline{X} - \overline{Y}) = \frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2^2} \] Since standard deviation is the square root of variance, it follows that: \[ \sigma_{\overline{X} - \overline{Y}} = \sqrt{V(\overline{X} - \overline{Y})} \] Options for the expression: - \[ \sigma_{\overline{X} - \overline{Y}} = \sqrt{\frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2}} \] - \[ \sigma_{\overline{X} - \overline{Y}} = \sqrt{\frac{\sigma_1^2}{n_1} + \frac{\sigma_2^2}{n_2}^2} \] - \[ \sigma_{\overline{
**Educational Content on Flexural Strength Estimation**

### Data on Flexural Strength for Concrete Beams and Cylinders

#### Concrete Beams Flexural Strength (MPa)
- 5.1, 7.2, 7.3, 6.8, 6.5, 7.0, 6.3, 7.9, 9.0
- 8.4, 8.7, 7.8, 9.7, 7.4, 7.7, 8.0, 11.6, 11.3, 11.8, 10.7

#### Cylinders Strength Observations
- 6.5, 5.8, 7.8, 7.1, 7.2, 9.2, 6.6, 8.5, 7.0, 8.5
- 7.2, 8.1, 7.4, 8.5, 8.9, 9.9, 12.6, 11.2, 6.9, 11.4

### Prior Considerations for Data Analysis

- **Beam Strengths**: Denoted by X₁, ..., Xₘ
- **Cylinder Strengths**: Denoted by Y₁, ..., Yₙ
- Assume X's are a random sample from a distribution with mean μ₁ and standard deviation σ₁.
- Assume Y's are a random sample from another distribution with mean μ₂ and standard deviation σ₂.

### Analysis

#### Task (a): Demonstrate that X̄ – Ȳ is an unbiased estimator of μ₁ – μ₂

Using rules of expected value:

Options:
1. \(E(X̄ - Ȳ) = (E(X) - E(Y)) = \mu_1 + \mu_2\)
2. \(E(X̄ - Ȳ) = (E(X) - E(Y))^2 = (\mu_1 - \mu_2)\)
3. \(E(X̄ - Ȳ) = (E(X) - E(Y)) = \frac{\mu_1 - \mu_2}{nm}\)
4. **\(E(X̄ - Ȳ) = (E(X) - E(Y
Transcribed Image Text:**Educational Content on Flexural Strength Estimation** ### Data on Flexural Strength for Concrete Beams and Cylinders #### Concrete Beams Flexural Strength (MPa) - 5.1, 7.2, 7.3, 6.8, 6.5, 7.0, 6.3, 7.9, 9.0 - 8.4, 8.7, 7.8, 9.7, 7.4, 7.7, 8.0, 11.6, 11.3, 11.8, 10.7 #### Cylinders Strength Observations - 6.5, 5.8, 7.8, 7.1, 7.2, 9.2, 6.6, 8.5, 7.0, 8.5 - 7.2, 8.1, 7.4, 8.5, 8.9, 9.9, 12.6, 11.2, 6.9, 11.4 ### Prior Considerations for Data Analysis - **Beam Strengths**: Denoted by X₁, ..., Xₘ - **Cylinder Strengths**: Denoted by Y₁, ..., Yₙ - Assume X's are a random sample from a distribution with mean μ₁ and standard deviation σ₁. - Assume Y's are a random sample from another distribution with mean μ₂ and standard deviation σ₂. ### Analysis #### Task (a): Demonstrate that X̄ – Ȳ is an unbiased estimator of μ₁ – μ₂ Using rules of expected value: Options: 1. \(E(X̄ - Ȳ) = (E(X) - E(Y)) = \mu_1 + \mu_2\) 2. \(E(X̄ - Ȳ) = (E(X) - E(Y))^2 = (\mu_1 - \mu_2)\) 3. \(E(X̄ - Ȳ) = (E(X) - E(Y)) = \frac{\mu_1 - \mu_2}{nm}\) 4. **\(E(X̄ - Ȳ) = (E(X) - E(Y
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