AS/A2 Stats 1 Stats 3

S2 Topic 1: Binomial and Poisson distributions
Binomial probabilites
Choose values for n and p and all the probabilites will be calculated and a chart of the probability distribution will be displayed. By choosing various values of n and p, decide how these values affect the symmetry of the distribution.

n: p:

Summary The Binomial distribution has two parameters, n and p. p is the probability of success n is the number of trials The distribution is perfectly symmetric when p = 0.5 The distribution is approximately symmetric when p is nearly 0.5 or when n is very large The distribution is skewed positively when p is small and negatively with p is large. A note about graphic calculators A graphic calculator, for example the TI-83 or similar model, can work out Binomial probabilities for you. Suppose that X ~ B(12,0.2): P(X=4) is given by binompdf(12,0.2,4)=.1328755507 P(X £ 4) is given by binomcdf(12,0.2,4)=.9274445005 A list of all the probabilites for the distribution B(12,0.2) is given by binompdf(12,0.2) © MathsNet 2001