You have two groups:

• Group 1: 8 observations, mean = 40, variance = 36
• Group 2: 12 observations, mean = 60, variance = 64

Using the variance decomposition formula: $\text{Total Var} = \frac{n_1}{n}s_1^2 + \frac{n_2}{n}s_2^2 + \frac{n_1}{n}(\bar{x}_1-\bar{x}_{total})^2 + \frac{n_2}{n}(\bar{x}_2-\bar{x}_{total})^2$

where the last two terms represent between-group variance, what is the total variance of the combined dataset?