459 / 762
Chapter 10: Sampling Distributions and the Central Limit Theorem
459
Note:
If the population variances are unknown but the sample sizes are
large (
> 30 and
> 30), then we can approximate the population
variances by the corresponding sample variances
and
. The
z
-score
will then be
Example 10-7:
Based on extensive use of two methods (Method 1 and
Method 2) of assembling a product, the following summary information, for
a random sample of the times (in minutes) it took to assemble the product
were obtained. The summary information for the samples is given in
Table
10-14.
In addition, based on historical information, the means for the two
populations are estimated to be 85 and 76 respectively.
Table 10-14:
Information related to
Example 10-7