Question

I really need help. Please!
In a SRS of 80 teenagers, the average number of text messages received per day is found to 50. If the standard deviation of number of texts received is known to be σ = 12, find the 95% confidence interval for the number of text messages received

Answer 1

Find out the value of +/- Z that enclose 95% of the area under the normal distribution curve.
using
\(Z=(x-\mu)/\sigma\), => \(x=\sigma Z+\mu\)
find the upper and lower limits of x, corresponding to +Z and -Z respectively.

Answer 2

@mathmate
Just to be sure are my numbers right to solve the problem?
(80-50)/12=2.5
12(1.96)+80=103.52

Answer 3

You need to first find Z that encompasses 95% of the area under the normal distribution curve.
Use help from the following link, if necessary.
https://www.mathsisfun.com/data/standard-normal-distribution.html