What the heck is a binomial setting?!
*It has a fixed number of independent trials!
*It has a fixed probability of success!
*Observations can be classified as either success or failure!
*AND...if n is large we can just assume it's binomial!!!
Let's do some notation!
*B(n,p) is a binomial distribution for the count X of successes where n is the number of observations and p is the probability of a success on any single observation!
Get your calculator out!
*To get individual probabilities!:
binompdf(n,p,X) can help us find stuff like P(X=1) or P(X=2)! Yeah!
So let's do some stats!
Roll a die 20 times and count the number of 3's! Find P(X=7)!
binompdf (20, 1/6, 7) = .0259!!!!!
*To get cumulative probabilities!:
binomcdf(n,p,X) gives us the sum of probabilities up to X! (YES THIS
INCLUDES X!!) We can find stuff like P(X<1) or
P(X<2)!
Fish on?!
Roll a die 20 times and count the number of 3's! Find P(X<4)!
binomcdf(20, 1/6, 4) = .7687!
Now find P(X>4)!
1-P(X<4)
= 1-binomcdf(20,
1/6, 4) = 1-.7687
= .2313!
What if the calculator breaks?!
Binomial Formula for k successes!:
P(X=k) = n! {p^k (1-p)^(n-k)}
k!(n-k)!
Other formulas!:
*mean = np
*variance = np(1-p)
*standard deviation =
It looks pretty normal to me...!
Conditions for approximating binomial functions as normal!:
*n must be large and the conditions np>10 and n(1-p)>10
must be met!
*Then we can say X is approx. N(np, )
and use normalcdf(min, max, mean, st. dev.)!