alevel statistics variance question HELP URGENT Watch
The lengths of 45 ropes used at an outdoor recreational center can be extended by 30% when stretched. the sum of squares of their stretched lengths is 0.0507km^2 and their natural lengths, x metres, are summarized by ∑(x-20)^2=1200. find the mean natural length of these 45 ropes.
Sum x^2 = 50700/1.3^2 = 30000
Var(X) = Var(X - 20)
(Sum x^2)/n - u^2 = [Sum (x - 20)^2]/n - (u - 20)^2
Solve for u, you'll get an integer