To Construct an Interval Estimate for the Difference Between the Means

Multiple Choice

To construct an interval estimate for the difference between the means of two populations when the standard deviations of the two populations are unknown, we must use a t distribution with (let n₁ be the size of sample 1 and n₂ the size of sample 2) _____ degrees of freedom.

A) n₁ + n₂
B) n₁ + n₂ - 1
C) n₁ + n₂ - 2
D) n₁ - n₂ + 2