The postal service groups first-class mail as letters, cards, flats, or parcels. Over a period of three weeks, one item of each kind was sent from a particular postal administrative center. The total time in transit was recorded. A statistical software package was then used to perform the analysis. The results follow.

Source.............. DF.......... SS......... MS........... F............. P

Factor................ 3........ 13.82......... 4.61......... 2.72..... 0.051

Error................ 68....... 115.17......... 1.69

Total................. 71....... 128.99

S = 1.301......... R-Sq = 10.71%............... R-Sq(adj) = 6.77%

Individual 95% CIs for Mean Based on Pooled StDev

Use the .05 significance level to test if this evidence suggests a difference in the means for the different types of first-class mail.

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N Mean StDev Level Letters 18 1.444 1.097(*) Cards 18 1.6671.455 Flats 18 2.4441.617 Parcels 18 2.3890.916 1.20 1.80 2.40 3.00