The Circumference of a Species of Tree Was Thought to Be

Multiple Choice

The circumference of a species of tree was thought to be different depending on certain geographical factors. An SRS of 60 trees of this species is selected in Sequoyah National Forest, where it is found that x̄₁= 6 meters with a standard deviation S₁= 3 meters. A second SRS of size 40 trees of the same species is independently selected in Yellowstone National Forest, and it is found that x̄₂= 4 meters with a standard deviation S₂= 2 meters. Let μ₁ and μ₂ represent, respectively, the true mean circumferences of this species of tree. Assume the two-sample t procedures are safe to use. What is a 95% confidence interval for μ₁ - μ₂ based on these data?

A) 2 ± 0.50 m
B) 2 ± 0.84 m
C) 2 ± 0.99 m
D) 2 ± 1.34 m