How do you read a cumulative binomial probability table?

1 Answer
Nov 26, 2017

Cumulative binomial probability tables give are used to find P(X<=x) for the distribution X~B(n,p)

Using some basic rules you can work out many different probabilities of a binomial distribution:
P(X < x) = P(X <= x-1)
P(X >= x)= 1-P(X <= x-1)
P(X > x)= 1-P(X <= x)
P(A < X <= B) = P(X <=B) - P(X <= A)
... and so on.

There is a seperate table for each sample size ("n") so first find the correct table of n=your sample size.

Then find the column on that table with the probability "p" of your distribution. The the number in the row x=a is P(X <=a )

ie. to find P(4 <= X <= 9) for the the distribution X~B(14, 0.55), go to the table for n=14. Then find the column p=0.55. Look for the row x=9 in that column, which gives 0.8328, and then look for x=3 in that column, which gives 0.0114.
So P(4 <= X <= 9) = 0.8328-0.0114=0.8214