Starbucks had found that 24 of customers purchase more than

Starbucks had found that 24% of customers purchase more than one cup of coffee per day from their shops. Suppose you randomly choose 200 of today\'s Starbucks customers.

Find the probability that no less than 30% of them purchased more than one cup of coffee from Starbucks.

Solution

Normal Distribution
Proportion ( P ) =0.24
Standard Deviation ( sd )= Sqrt (P*Q /n) = Sqrt(0.24*0.76/200) = 0.0302
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
P(X < 0.3) = (0.3-0.24)/0.0302
= 0.06/0.0302= 1.9868
= P ( Z <1.9868) From Standard Normal Table
= 0.9765                  
P( X>=0.3 ) = 1 - P(X < 0.3) = 1 - 0.9765 = 0.0235