Assume that when adults with smartphones are randomly selected, 42% use them
in meetings or classes. If 8 adult smartphone users are randomly selected,
find the probability that at least 5 of them use their smartphones in
meetings or classes.
Got a TI-83 or 84?
On those calculators binomcdf( calculates for n trials, the probability that
there will be a certain number or fewer successes. Since this is a "5 or
more" problem, we have to find the probability of the complement event "4 or
fewer", and subtract it from 1.
The complement event of
"at least 5 of the 8 use their smartphones in meetings or classes"
is
"4 or fewer of the 8 use their smartphones in meetings or classes."
So type in "1-" on the main screen so that what we get will be subtracted from 1.
You'll find binomcdf( by pressing 2ND then VARS and scrolling down to it.
That's 8 trials, p: is 0.42, and the x-value is 4, you should make sure
that you see this on your screen:
1-binomcdf(8,0.42,4)
then press ENTER.
Answer: 0.206164373
Edwin