4 Delip measured the speeds, \(x \mathrm {~km}\) per hour, of 70 cars on a road where the speed limit is 60 km per hour. His results are summarised by \(\Sigma ( x - 60 ) = 245\).
- Calculate the mean speed of these 70 cars.
His friend Sachim used values of \(( x - 50 )\) to calculate the mean.
- Find \(\Sigma ( x - 50 )\).
- The standard deviation of the speeds is 10.6 km per hour. Calculate \(\Sigma ( x - 50 ) ^ { 2 }\).