1 A summary of 20 values of \(x\) gives
$$\Sigma ( x - 30 ) = 439 , \quad \Sigma ( x - 30 ) ^ { 2 } = 12405 .$$
A summary of another 25 values of \(x\) gives
$$\sum ( x - 30 ) = 470 , \quad \sum ( x - 30 ) ^ { 2 } = 11346 .$$
- Find the mean of all 45 values of \(x\).
- Find the standard deviation of all 45 values of \(x\).