Probablility/STATS

Question

The average composite ACT score for Ohio students who took the test in 2003 was 21.4. Assume that the standard deviation is 1.05. In a random sample of 25 students who took the exam in 2003, what is the probability that the average composite ACT score is 22 or more? which sampling distribution used?

Answer 1

Since the sample size is less than 30 you should use a t-distribition.

 

t = (x-mu) / sigma

  = (22 - 21.4)/[1.05/sqroot(25)]

 

look up this in a t-dist table, see:

 

https://www.wyzant.com/resources/files/393113/t_distribution

 

to get the probability.

 

 

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