Red Street Garage has 9 used cars for sale. Fairwheel Garage has 15 used cars for sale. The mean age of the cars in Red Street Garage is 3.6 years and the standard deviation is 1.925 years. In Fairwheel Garage, Σx = 64 and Σx^2 = 352, where x is the age of a car in years.

(i) Find the mean age of all 24 cars.

(ii) Find the standard deviation of the ages of all 24 cars.

Please do tell me what does Σx and Σx^2 means. I just started with these things so every help is appreciated. If you could show it step-by-step I'd appreciate it much.

Thanks in advance,

idocoldplay