Question

The GE company also makes light bulbs. They claim that their bulbs last an average of 750 hours, with a standard deviation of 20 hours. A random sample of 64 light bulbs is taken.

Make sure to first find Z for each using z = (x -mean)/stdev

mean = 750
stdev=20
a. What is the probability that xbar > 750?
b. What is the probability that 745 < xbar < 755?
c. What is the probability that xbar < 735?

*On this problem, you may be tempted to think of this in terms of means rather than individual data.

What you are seeing is the CLT. I am organizing the data into sub groups and using the mean to describe each subgroup.

The three important points are:

The mean of the subgroup means is the same as the mean of the population
The stdev the mean sub groups is the population stdev divided by the square root of sample size
As I collect more and more data, the behavior will be normal

Answer 1