Question

1. Assume that a typical college student in the US sends 75 text messages a day with a standard deviation of 12 text messages. If we take a random sample of 40 college students, what is the probability that this group will send an average (x-bar) of 78 or more messages, tomorrow?

Answer 1

Solution :

Given that,

mean = = 75

standard deviation = = 12

n=40

= =75

= / n = 12 / 40 = 1.8973

P( > 78) = 1 - P( < 78)

= 1 - P[( - ) / < (78-75) /1.8973 ]

= 1 - P(z <1.58 )

Using z table

= 1 - 0.9429

= 0.0571

probability= 0.0571