text: What is n?  a variable?\nsum of i^2 from 1 to N is (N*(N+1)*(2N+1))/6\nsum of i from 1 to N is N(N+1)/2\n(i^2-2i)/n = (1/n)[i^2 - 2i]\n= (1/n)[(N*(N+1)*(2N+1))/6 - 2N(N+1)/2]\n= (1/n)[(N*(N+1)*(2N+1))/6 - N(N+1)]\nRplace N with 15\n(1/n)[(15*(15+1)*(2*15+1))/6 - 15(15+1)]\n= (1/n)[(15*16*31)/6 - 15(16)]\n= (1/n)[1240 - 240]\n= (1/n)(1000)\n= 1000/n