# statistics help now 1

##### Question 1 of 20
1.0 Points
Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation).
NOTE: For scientific notation, a period MUST be used as the decimal point marker.

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values.

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not.

You are trying to estimate the average amount a family spends on food during a year. In the past, the standard deviation of the amount a family has spent on food during a year has been
\$1200. If you want to be 99% sure that you have estimated average family food expenditures within \$60, how many families do you need to survey?  Place your answer, a whole number, in the blank

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##### Question 9 of 20
1.0 Points
A sample of 23 European countries found that the variance of life expectancy was 7.3 years. What is the 95% confidence interval estimate for the variance of life expectancy in Europe?

##### Question 10 of 20
1.0 Points
In constructing a confidence interval estimate for a population mean, when we replace
with the sample standard deviation (s), we introduce a new source of variability and the sampling distribution we use is:

##### Question 11 of 20
1.0 Points
Find the 95% confidence interval for the standard deviation of the lengths of pipes if a sample of 26 pipes has a standard deviation of 10 inches.

##### Question 12 of 20
1.0 Points
If you are constructing a confidence interval for a single mean, the confidence interval will___________ with an increase in the sample size.

##### Question 13 of 20
1.0 Points
The average gas mileage of a certain model car is 26 miles per gallon. If the gas mileages are normally distributed with a standard deviation of 1.3, find the probability that a randomly selected car of this model has a gas mileage between 25.8 and 26.3 miles per gallon.

##### Question 14 of 20
1.0 Points
Confidence intervals are a function of which of the following three things?

##### Question 15 of 20
1.0 Points
The t- distribution for developing a confidence interval for a mean has _____ degrees of freedom.

##### Question 16 of 20
1.0 Points
A researcher wishes to know, with 98% confidence, the percentage of women who wear shoes that are too small for their feet. A previous study conducted by the Academy of Orthopedic Surgeons found that 80% of women wear shoes that are too small for their feet. If the researcher wants her estimate to be within 3% of the true proportion, how large a sample is necessary?

##### Question 17 of 20
1.0 Points
From a sample of 500 items, 30 were found to be defective. The point estimate of the population proportion defective will be:

##### Question 18 of 20
1.0 Points
Which of the following will make a confidence interval narrower and more precise?

 Part 3 of 3 –

##### Question 19 of 20
1.0 Points
The 95% confidence interval for the population mean
, given that the sample size n = 49 and the population standard deviation
= 7, is
.

##### Question 20 of 20
1.0 Points
As a general rule, the normal distribution is used to approximate the sampling distribution of the sample proportion,
, only if the sample size n is greater than 30.