Standard Deviation Questionnaire

Find P(Z ? 1.8). Round answer to 4 decimal places. Answer:

Question 2 (1 point)

Question 2 options:

Find P(-1.96 ? Z ? 1.96). Round answer to 2 decimal places. Answer:

Question 3 (1 point)

Saved

Question 3 options:

A dishwasher has a mean life of 12 years with an estimated standard deviation of 1.25 years (“Appliance life expectancy,” 2013). Assume the life of a dishwasher is normally distributed. Find the number of years that the bottom 25% of dishwasher would last. Round answer to 2 decimal places. Answer:

Question 4 (1 point)

Find the probability that

$?$

Shaded graph that extends from 0 to 8.5 shaded up to 5. X axis goes from 0 to 10 and y-axis is labeled with 1/8

Question 4 options:

	0.438
	0.625
	0.125
	0.5

Question 5 (1 point)

The manufacturer of a new compact car claims the miles per gallon (mpg) for the gasoline consumption is mound-shaped and symmetric with a mean of 24.6 mpg and a standard deviation of 9.5 mpg. If 30 such cars are tested, what is the probability the average mpg achieved by these 30 cars will be greater than 28?

Answer: ___ Round your answer to 4 decimal places as necessary. For example, 0.1357 would be a legitimate entry. Make sure you include the 0 before the decimal.

___

Question 5 options:

Question 6 (1 point)

The average lifetime of a set of tires is three years. The manufacturer will replace any set of tires failing within two years of the date of purchase. The lifetime of these tires is known to follow an exponential distribution. What is the probability that the tires will fail within two years of the date of purchase?

Question 6 options:

	0.8647
	0.2212
	0.4866
	0.9997

Question 7 (1 point)

The average lifetime of a certain new cell phone is three years. The manufacturer will replace any cell phone failing within two years of the date of purchase. The lifetime of these cell phones is known to follow an exponential distribution. The decay rate is:

Question 7 options:

	0.1666
	0.6666
	0.3333
	0.5000

Question 8 (1 point)

Question 8 options:

The caller times at a customer service center has an exponential distribution with an average of 10 seconds. Find the probability that a randomly selected call time will be less than 25 seconds? (Round to 4 decimal places.) Answer:

Question 9 (1 point)

Suppose that the longevity of a light bulb is exponential with a mean lifetime of eight years. Seventy percent of all light bulbs last at least how long?

Question 9 options:

	0.1175
	0.1859
	9.6318
	0.3034
	0.3682

Question 10 (1 point)

Question 10 options:

The waiting time for a taxi has a uniform distribution between 0 and 10 minutes. What is the probability that the waiting time for this taxi is less than 7 minutes on a given day? Answer: (Round to two decimal place.)

Question 11 (1 point)

Question 11 options:

Miles per gallon of a vehicle is a random variable with a uniform distribution from 25 to 35. The probability that a random vehicle gets between 25 and 34 miles per gallon is: Answer: (Round to one decimal place)

Question 12 (1 point)

Question 12 options:

The mail arrival time to a department has a uniform distribution over 0 to 60 minutes. What is the probability that the mail arrival time is more than 20 minutes on a given day? Answer: (Round to 2 decimal places.)

Question 13 (1 point)

Question 13 options:

The waiting time for a bus has a uniform distribution between 0 and 10 minutes. What is the probability that the waiting time for this bus is less than 5 minutes on a given day? Answer: (Round to two decimal place.)

Question 14 (1 point)

Question 14 options:

Miles per gallon of a vehicle is a random variable with a uniform distribution from 25 to 35. The probability that a random vehicle gets between 25 and 30 miles per gallon is: Answer: (Round to two decimal place)

Question 15 (1 point)

Question 15 options:

A local pizza restaurant delivery time has a uniform distribution over 0 to 60 minutes. What is the probability that the pizza delivery time is more than 30 minutes on a given day? Answer: (Round to 2 decimal place.)

Question 16 (1 point)

Question 16 options:

The MAX light rail in Portland, OR has a waiting time that is normally distributed with a mean waiting time of 5 minutes with a standard deviation of 2.9 minutes. A random sample of 40 wait times was selected, what is the probability the sample mean wait time is under 4 minutes? Round answer to 4 decimal places. Answer:

Question 17 (1 point)

Question 17 options:

The final exam grade of a statistics class has a skewed distribution with mean of 76 and standard deviation of 7.6. If a random sample of 32 students selected from this class, then what is the probability that average final exam grade of this sample is between 75 and 80? Answer: (round to 4 decimal places)

Question 18 (1 point)

Question 18 options:

The average amount of water in randomly selected 16-ounce bottles of water is 16.1 ounces with a standard deviation of 0.5 ounces. If a random sample of thirty-six 16-ounce bottles of water are selected, what is the probability that the mean of this sample is less than 15.9 ounces of water? Answer: (round to 4 decimal places)

Question 19 (1 point)

Question 19 options:

The time a student sleeps per night has a distribution with mean 6.3 hours and a standard deviation of 0.6 hours. Find the probability that average sleeping time for a randomly selected sample of 42 students is more than 6.5 hours per night. Answer: (round to 4 decimal places)

Question 20 (1 point)

Question 20 options:

The time a student sleeps per night has a distribution with mean 6.1 hours and a standard deviation of 0.6 hours. Find the probability that average sleeping time for a randomly selected sample of 36 students is more than 6 hours per night. Answer: (round to 4 decimal places)