a) 1+2+...+400= (400x401):2= 100x802 (Suma lui Gauss)
Impartirea de la prima vine astfel:
(100x802):802=100
b) Dam factor comun in ambele paranteze, in prima 6 in a 2 a dam factor comun 3:
6x(1+2+3+...+52):3x(1+2+...+52)=
6 impartit la 3= 2
=> (2x (52x53):2) : (52x53):2=
= (52x53):(26x53)= 2