$$T_assy = \sqrt0.20^2 + 0.10^2 + 0.15^2$$ $$T_assy = \sqrt0.04 + 0.01 + 0.0225$$ $$T_assy = \sqrt0.0725$$ $$T_assy = 0.269 \text mm$$
$$T_assy = \sqrt\sum_i=1^n (C_i \cdot T_i)^2$$ rss method tolerance analysis
Where is a correction factor (typically 1.2 to 1.5 ), or using the Benderization method: $$T_assy = \sqrt0