In: Statistics and Probability
underneath the cap of brand x cola bottles is a chance to win a free cola. suppose that the probability of winning is 1 out of 11 when you buy 16 colas. what is the probability of winning at least once?
Probability of winning a free cola : p = 1/11
Probability of not a winning a cola : q = 1-1/11 = 10/11
Number of colas bought n : =16
X : Number times won a free cola
probability of winning at least once = P(X1)
P(X1) = 1-P(X<1) = 1-P(X=0)
P(X=0) i.e Probability of losing for all the 16 bottles bought
Probability of losing when one bottle is bought = 10/11
Probability of losing for all the 16 bottles bought =P(X=0) = (10/11)16
probability of winning at least once = 1- (10/11)16
Another Method .
we use Binomial distribution to solve .
X : Number times won a free cola;
X is a binomial distribution with n= 16 and p =1/11
And the probability mass function =
probability of winning at least once = P(X1)
P(X1) = 1-P(X<1) = 1-P(X=0)
P(X1) = 1-P(X<1) = 1-P(X=0) = 1 - (10/11)16 = 0.782371
Probability of winning at least once = P(X1) = 0.782371
Probability of winning at least once = 0.782371