Posted by Joy on .
Shown below are the data giving the length of life of lights in an underground tunnel.
9.0 months 7.0 months
8.2 months 8.3 months
7.8 months 8.1 months
7.5 months 7.6 months
9.1 months 7.4 months
I calculated the standard deviation to be about 0.679.
Estimate the probability that a random chosen light will last as long as 7 months after installation. Assume the data to be described by a normal distribution.
Can anyone help me with the process I would use to calculate the answer? Thanks!

science 
PsyDAG,
I assume that you have calculated the mean to find the SD.
Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to the Z score.