A dangerous computer virus attacks a folder consisting of 250 files. Files
are affected by the virus independently of one another. Each file is
affected with the probability 0.032. What is the probability that more than
7 files are affected by this virus?
n is your sample size, 250
p is your given probability, 0.032
q is 1 - p, q = 1 - 0.032 = 0.968
When n∙p and n∙q are greater than 5, you can use the normal approximation
to the binomial to solve a problem.
n∙p = 250∙0.032 = 8 and n∙p = 250∙0.968 = 242, and they are both greater
than 5, so we can use the normal approximation to the binomial.
On your TI-84, press 2ND VARS 2
normalcdf
lower:7
upper:1E99 <--to get the "E", press 2ND and then the comma key.
μ:8
σ:2.78894341
paste <--scroll to highlight "paste" using down arrow key.
Press enter
See this:
normalcdf(7,1E99,8,2,2.78804341)
Press enter
See this:
0.6400806277 <--answer, round to 0.64
Edwin
