What is the probability of drawing a sample with a z value of -5 or less. Answer

Question

What is the probability of drawing a sample with a z value of -5 or less. Answer to four decimal places 0.3085 QUESTION 18 Your results show that the (estimated) standard error is 1.95 from a sample of n=52. In this case though a coworker wants to know what the original standard deviation was. Work backwards and find the sample standard deviation. Answer to three decimal places 14.062 QUESTION 19 You take a sample of 33 textbooks in the bookstore and find the standard deviation is 48.1 (in dollars). What is the (estimated) standard error? Answer to two decimal places. 8.37 QUESTION 20 Suppose you have the average price used textbooks. This comes from a sample of 20 different used and college book stores in southern California. Suppose that the population standard deviation for the prices is 18.5 and that the distribution is of prices is normal. If the population mean is 141.3, what is the z value for a sample average of 119.9? Answer to two decimal places. 5.17

Explanation / Answer

Q17.
P(X < -0.5) = (-0.5-0)/1
= -0.5/1= -0.5
= P ( Z <-0.5) From Standard Normal Table
= 0.3085

Q18.
stanadard error = sd/ sqrt(n)
where,
sd = population standard deviation
n = population size
stanadard error = ( sd/ sqrt ( 52) )
1.95 = ( sd/ sqrt ( 52) )
sd = 1.95 * sqrt ( 52)
sd = 14.062

Q19.
stanadard error = sd/ sqrt(n)
where,
sd = population standard deviation
n = population size
stanadard error = ( 48.1/ sqrt ( 33) )
= 8.373

Q20.
P(X = 119.9) = (119.9-141.3)/18.5
= -21.4/18.5= -1.1568 ~ -1.16

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