Which formula is used when variances are unequal?

• A. t_calculated = (x₁ - x₂) / (s₁ + s₂)
• B. t_calculated = (x₁ - x₂) / √((s₁²/n₁) + (s₂²/n₂))
• C. t_calculated = (x₁ - x₂) / s₁
• D. t_calculated = (x₁ - x₂) / s_pooled

Answer: (B)