Answer:
υ= 25
Step-by-step explanation:
IF we have two small independent samples from two normal populations with means μ1 and μ2 and standard deviations σ1 and σ 2 but unknown ,then the unbiased pooled or combined estimate of the common variance sigma square ha s student's t distribution with degrees of freedom given by
υ= n1+ n2- 2
In the given question
Sample A size= n1= 12
Sample B size = n2= 15
υ= 12+15-2
υ= 25
where
sp²= (n1-1) s1² + (n2-1) s2² / n1+n2-2
