in clasa x elevi
strangeri de mana :
eu colegul 1 colegul 2 ............................ ultimul coleg :
⇵ ⇵ ⇵ ⇵
( x -1) + ( x -2) + ( x -3) + ........................ + 1 = 190
suma Gauss: ( x -1 + 1) ·(x -1) / 2 = 190 inmultim cu 2
x · ( x -1) = 380
numere consecutive
x · ( x -1) = 20 · 19
⇒ in clasa sunt x =20 elevi