Suppose a research firm conducted a survey to determine the mean amount 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) 1.0000

Question

Quizplus · Accepted Answer

The sample mean is $20 with a standard deviation of $5. For a sample size of 100, the standard error is $5/√100 = $0.5. Using the standard normal distribution, the z-scores for $19 and $21 are -2 and 2, respectively. The probability of z being between -2 and 2 is approximately 0.9544.

Suppose a Research Firm Conducted a Survey to Determine the Mean