The second cross-product entry is $A_{12}=\sum_{i,j}X_{ij}$. Regressing earned on the ten person indicators without an intercept makes $(g_x)_i$ the mean of that person's ten earned values. Therefore
$$
\sum_i(g_x)_i=\frac1{10}\sum_{i,j}X_{ij}=0.1A_{12}.
$$


Solution

Past exam of the mathematics course of the University of Cambridge / 2025 / iii / Paper 218 / 5 / d / ii / Solution

 Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2025/iii/paper-218/5/d/ii/solution