\text { 4. Show that if } k_{i}=\left(X_{i}-\bar{X}\right) /\left[\sum\left(X_{i}-\bar{X}\right)^{2}\right], \text { then } \text { (a) } \sum k_{i}=0 \text { (b) } \left.\sum k_{i}^{2}=1 / \Sigma\left(X_{i}-\bar{X}\right)^{2}\right] \text { (c)
} \sum k_{i}\left(X_{i}-\bar{X}\right)=\sum k_{i} X_{i}=1