Q.1. An advertising company wants to estimate with 98% confidence interval, the number of times a website is hit during an hour. It is determined that = 26. How large a sample should the company take, if it wishes that the margin of error should not exceed 10?

Q.2. If we take a sample from an infinite population, what will happen to the standard error of the mean when the sample size is increased from 60 to 240?

Q.3. A sample of 16 Ten-Years old girls had a mean weight of 71.54 pounds and a standard deviation of 12 pounds.

(a) What assumption is necessary for the validity of the confidence interval constructed?

(b) What is the estimated standard error?

(c) Construct a 95% confidence interval for the population mean.

Q.5. In measuring reaction time, a psychologist estimated that standard deviation is 0.05 seconds. How large a sample of measurements must be taken in order to 95% confident that the error in his estimate of mean reaction time will not exceeds 0.01 seconds.

Q.6. A random sample of 20 boys was taken to estimate the 98% confidence interval for the mean weight of boys aged between 14 to 15 years. The 98% confidence interval was found to be 45.5 < < 51.3. Find the sample mean and sample variance.

Q.7. The following results are obtained in an IQ - TEST taken by 50 boys and 60 girls: BOYS GIRLS X1 = 4910 X2 = 5676 X1 2 = 483515 X2 2 = 537481 Construct the 95% Confidence Interval for the difference between the IQ-TEST of Boys and Girls.

Q.8. The following data were obtained from an experiment designed to estimate the reduction in Blood Pressures as a result of following a salt free diet for two weeks: BEFORE 93 106 87 92 102 95 88 110 AFTER 92 102 89 92 101 96 88 105 Assuming that the Blood Pressures of the population are normally distributed, find the 98% confidence interval for the mean reduction in Blood Pressures.