\\\\(P = 1 - 6 \\dfrac{\\sum di^2}{n(n^2 - 1)}\\\\)\\\\(0.6 = 1 - \\dfrac{6 \ imes 66}{n(n^2 - 1)}\\\\)\\\\(\\dfrac{6 \ imes 66}{n(n^2 - 1)} = 0.4 \\\\)\\\\(n(n^2 -1) = \\dfrac{3}{2} \ imes 66 \ imes 10 = 990\\\\)\\\\(n = 10 \\\\)\\\\(10(10^2 - 1) = 10 (99) = 990\\\\)