# Question: A certain unnamed statistics teacher needs to grade 90 exams

A certain unnamed statistics teacher needs to grade 90 exams. The teacher claims that exams require an average of 12 minutes to grade with a standard deviation of 3 minutes. A random sample of 15 exams is selected.

a. What is the probability that the sample mean will be more than 11 minutes per exam?

b. What is the probability that the sample mean will be more than 12.5 minutes per exam?

c. Suppose the sample mean is 10 minutes. Is the teacher’s claim valid according to this sample?

d. What assumptions need to be made in this problem?

a. What is the probability that the sample mean will be more than 11 minutes per exam?

b. What is the probability that the sample mean will be more than 12.5 minutes per exam?

c. Suppose the sample mean is 10 minutes. Is the teacher’s claim valid according to this sample?

d. What assumptions need to be made in this problem?

## Relevant Questions

Shortly after the major oil spill in the Gulf of Mexico that occurred in April 2010 due to an explosion on an oil rig, a Rasmussan Poll found that 23% of respondents were against offshore drilling for oil. In an effort to ...The “sandwich generation” is defined as adults who are financially supporting their children while providing care for their aging parents. The number of adults in this category has increased recently with higher ...Obtaining a driver’s license at the earliest eligible age has been a teenage ritual that appears to be fading. A study performed by the University of Michigan Transportation Research Institute recently found that 30% U. S. ...For a population that is left skewed with a mean of 24 and a standard deviation equal to 15, determine the probability of observing a sample mean of 23 or more from a sample of size 32. Construct a 90% confidence interval to estimate the population mean using the following data: x = 25 σ = 5.2 n = 21 What assumptions need to be made about this population?Post your question