Calculate the Degrees of Freedom Associated with a Small-Sample Test $\left( \mu _ { 1 } - \mu _ { 2 } \right)$

Multiple Choice

Calculate the degrees of freedom associated with a small-sample test of hypothesis for $\left( \mu _ { 1 } - \mu _ { 2 } \right)$ , assuming $\sigma _ { 1 } ^ { 2 } \approx \sigma _ { 2 } ^ { 2 }$ and $n _ { 1 } = n _ { 2 } = 20$

A) 30
B) 15
C) 31
D) 33