Standard error of the Sample M

fian

2008-12-20 6:41 am

請教以下題目:

1.1 A random sample of 36 students shows an average age of 24 years old with a known poplation standard deviation of 6 years.

the standard error of the sample mean is ??

1.2 The probability of obtaining a sample mean large than 26 is ??

2.1 Suppose the during any hour in a large department store, the mean nos of shoppers is 448, with a standard deviation of 21 shoppers. The probability that a random sample of 49 different shopping hours will yield a sample mean less than 446 shoppers is ??

2.2 The probability that a random sample of 49 different shopping hours will yield a mean between 441 and 446 shoppers is ??

求以上答案及公式, 謝!

回答 (1)

myisland8132

2008-12-21 2:40 am

✔ 最佳答案

1
the standard error of the sample mean
=6/√36
=1
1.2
P(X>26)
=P[(X-24)/1>(26-24)/1]
=P(Z>2)
=0.02275
2.1
μ= 448 σ=21,s=3
P(X<446)
=P[(X-446)/3<(446-448)/3]
=P(Z<-2/3)
=0.252493
2.2
P(441<X<446)
=P[(441-448)/3<(X-446)/3<(446-448)/3]
=P(-7/3<Z<-2/3)
=0.242677

2008-12-20 18:41:43 補充：
sample standard deviation=population standard deviation/√sample size

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