Devry Math 221 Week 7 Quiz with Formulas – Latest

DeVry MATH 221 Week 7 Quiz with Formulas – Latest

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1. A mechanic sells a brand of automobile tire that has a life expectancy that is normally distributed, with a mean life of 35,000 miles and a standard deviation of 2800 miles. He wants to give a guarantee for free replacement of tires that don’t wear well. How should he word his guarantee if he is willing to replace approximately 10% of the tires?

Tires that wear out by 31,412 miles will be replaced free of charge.

Hint:

Here we need a value of X say K such that P (X < K) = 0.10

We know P (Z < -1.282) = 0.10

Thus from Z score of K we have,

Solving for K we have K = 31412

2. Find the indicated z-score shown in the graph to the right.

The z-score is -1.18

Hint:

From standard normal table, P (Z < -1.18) = 0.1190

Therefore, z = -1.18

3. A researcher wishes to estimate, with 95% confidence, the amount of adults who have high-speed internet access. Her estimate must be accurate within 4% of the true proportion.

a) find the minimum sample size needed, using a prior study that found that 32% of the respondents said they have high-speed internet access.

4. b) no preliminary estimate is available. Find the minimum sample size needed.a) = 523

b) = 601

Hint:

(a)

The sample size is given by where p = 0.32

Given that E = 4% = 0.04, = 1.959963985

Therefore, sample size,

That is, n >522.4384

Hence the minimum sample size required is n = 523

(b)

The sample size is given by where p = 0.50

Given that E = 4% = 0.04, = 1.959963985

Therefore, sample size,

That is, n >600.2279

Hence the minimum sample size required is n = 601

4. The total cholesterol levels of a sample of men aged 35-44 are normally distributed with a mean of 221 milligrams per deciliter and a...