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A consumer products company is formulating a new shampoo and interested in studying the mean foam height (in mm). Assume the foam height approximately follows a normal distribution with known variance of  σ2 = 400 mm2. A random sample of 9 such new shampoos results in a mean foam height 165 mm. Test if there is sufficient evidence to support the claim that the mean foam height of the new shampoo is different from 160.5 mm at α = 0.05. Which of the following statements is INCORRECT?

Question

A consumer products company is formulating a new shampoo and interested in studying the mean foam height (in mm). Assume the foam height approximately follows a normal distribution with known variance of  σ2 = 400 mm2. A random sample of 9 such new shampoos results in a mean foam height 165 mm. Test if there is sufficient evidence to support the claim that the mean foam height of the new shampoo is different from 160.5 mm at α = 0.05. Which of the following statements is INCORRECT?

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Solution

The question is asking to perform a hypothesis test to determine if there is enough evidence to support the claim that the mean foam height of the new shampoo is different from 160.5 mm.

Here are the steps to perform the hypothesis test:

Step 1: State the null hypothesis (H0) and the alternative hypothesis (H1). H0: μ = 160.5 mm (The mean foam height is 160.5 mm) H1: μ ≠ 160.5 mm (The mean foam height is not 160.5 mm)

Step 2: Determine the level of significance, α. In this case, α = 0.05.

Step 3: Calculate the test statistic. Since we know the population variance, we can use the z-test. The formula for the z-test is:

z = (X̄ - μ0) / (σ / √n)

where: X̄ is the sample mean = 165 mm μ0 is the population mean under the null hypothesis = 160.5 mm σ is the population standard deviation = √400 mm = 20 mm n is the sample size = 9

Substituting the values, we get:

z = (165 - 160.5) / (20 / √9) = 0.675

Step 4: Determine the critical value for a two-tailed test at α = 0.05. The critical values are -1.96 and 1.96.

Step 5: Compare the test statistic with the critical value. Since -1.96 < 0.675 < 1.96, we do not reject the null hypothesis.

Therefore, there is not enough evidence to support the claim that the mean foam height of the new shampoo is different from 160.5 mm at α = 0.05.

The incorrect statement would be "There is sufficient evidence to support the claim that the mean foam height of the new shampoo is different from 160.5 mm at α = 0.05."

This problem has been solved

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