Suppose a research firm conducted a survey to determine the average amount of money steady smokers spend on cigarettes during a week. A sample of 100 steady smokers revealed that the sample mean is $20 and the sample standard deviation is $5. What is the probability that a sample of 100 steady smokers spend between $19 and $21?
A) 0.4772
B) 0.0228
C) 0.9544
D) $20
E) None of the choices are correct

Question

Quizplus · Accepted Answer

The sample mean is $20, and the standard deviation of the sample mean (standard error) is $5/√100 = $0.5. Using the standard normal distribution, the probability that the sample mean is between $19 and $21 is calculated as P(-2 ≤ Z ≤ 2), which is approximately 0.9544.

Suppose a Research Firm Conducted a Survey to Determine the Average