Significant difference

#1
When does it apply regarding say MPG for American and Japnese cars:
Looking at lower and upper confidence levels I thought if they did not overlap there is not a significant difference. The question I missed was: Should the MPG population means for cars made in the two countries be considered significantly different? The answer was true. Any feedback would be great thanks. I think I am looking at this totaly wrong (ahem backwards).



a.) Japanese Cars
MPG
count 12

confidence interval 95.% lower 19.95
confidence interval 95.% upper 24.72
half-width 2.38



b.) American Cars
MPG
count 12

confidence interval 95.% lower 24.93
confidence interval 95.% upper 28.57
half-width 1.82