A toy manufacturer wants to see how long, on average, a new toy captures children's attention. He tests 17 children selected at random and finds that their mean attention span is 34 minutes with a standard deviation of 8 minutes. If we assume that attention spans are normally distributed, find a 99% Confidence interval for the mean attention span of children playing with this new toy. Then find the lower limit and upper limit of the 99% confidence interval. Carry your intermediate computations to at least three decimal places. Round your answers to one decimal place. (If necessary, consult a list of formulas.) Lower limit: ] ? Upper limit: I

A Surprising fact indicates that a small proportion of teens use a password on their mobile device. A poll chooses a simple random sample of 120 teens and asks if they use a password on their mobile device. The results showed that 56 of teens in our  sample used a password on their mobile device. Find a 90 % confidence interval for the proportion of teens who use a password on their mobile device. Interpret your confidence interval.

A statistics teacher taught a large introductory statistics class, with 500 students having enrolled over many years. The mean score over all those students on the first midterm was u = 88 with standard deviation o = 10. One year, the teacher taught a %3D much smaller class of only 25 students. The teacher wanted to know if teaching a smaller class was more effective and students performed better. We can consider the small class as an SRS of the students who took the large class over the years. The average midterm score was = 78. The hypothesis should be: a. Ho: H = 78 vs. Ha: H = 88. %3D O b. Ho: µ = 88 vs. Ha: µ 78 %3D Ο d. Ho: μ-88 νs. Ha: μ >88. %3D

A random sample of high school students is used to estimate the mean time all high school students study for Algebra II tests. A 99% confidence interval based on this sample is: 1.7 hours to 3.1 hours.  What is the sample mean?