Question

1supra 50 +3supra 50+5supra 50+......+51 supra 50=

Answer 1

1+3+...+51supra 50
1+3+..+51=(1+2+…+51)-(2+4+6+...+50)=
=(51•52):2-2(1+2+...+25)=
=2652:2-2((25•26):2)=
=1326-650=
=676 supra 50=13.25

Answer 2

 $...=\frac{1+3+5+...+51}{50}=\frac{26^2}{50}=676/50=13,52$