Question

Aflati media aritmetica a numerelor a si b
a= 1 supra 10 + 2 supra 11 + ... + 1991 supra 2000
b = 9 supra 10 + 9 supra 11 + ... + 9 supra 2000

Answer 1

a+b =(1/10 +9/10 ) +(2/11+9/11) +...+(1991/2000+9/2000) =
       = (10/10) +(11/11) +...+(2000/2000)=
        =1+1+...+1     (1991 termeni) 
         =1991
=> (a+b)/2 =1991/2