a + b = 1 700 cl
a - b = 25 dl = 250 cl
__________________
( a + b ) - ( a - b ) = 1 700 cl - 250 cl
a - a + b + b = 1 450 cl
2 × b = 1 450 cl
b = 1 450 cl : 2
b = 725 cl
a = 1 700 cl - 725 cl
a = 975 cl
Verific: 975 cl + 725 cl = 1 700 cl = 17 litri
Metoda grafica
a l----------l + 250 cl } suma lor = 1 700 cl
b l----------l
1 700 cl - 250 cl = 1 450 cl → suma celor 2 parti egale
1 450 : 2 = 725 ( b )
725 + 250 = 975 ( a )