Question

According to some current research, the average number of different apps launched per day for all smartphone users is 9 per day and the standard deviation is 3 per day. In a simple random sample of 100 smartphone users, what is the probability that the sample mean number of different apps launched per day is less than 8?

Answer 1

Solution :

Given that ,

mean = = 9

standard deviation = = 3

n = 100

= = 9 and

= / n = 3/ 100 = 0.3

P( < ) =   P(( - ) / < (8 - 9) / 0.3)

= P(z < -3.33)   Using standard normal table.   

Probability = 0.0004