Question

Qdoba Customers have a 0.42 probability of buying drink. Of the next 21 customers, what is the probability that equal to 9 of them will buy Coke? Round you answer to 2 decimal places.

Answer 1

Solution:

Given that,

P = 0.42

1 - P = 0.58

n = 21

Here, BIN ( n , P ) that is , BIN (21 , 0.42)

According to normal approximation binomial,

X Normal

Mean = = n*P = 8.82

Standard deviation = =n*p*(1-p) = 5.1156

We using continuity correction factor

P(X = a) = P( a - 0.5 < X < a + 0.5)

P(8.5 < x < 9.5) = P((8.5 - 8.82)/ 5.1156) < (x - ) /  < (9.5 - 8.82) / 5.1156) )

= P(-0.14 < z < 0.30)

= P(z < 0.30) - P(z < -0.14)

= 0.6179 - 0.4443

Probability = 0.1736