Răspuns :
3a+2b = 87 ; a+b = 36 ; b = 36-a ; inlocuim b in prima relatie
3a+2(36-a) = 87 ; 3a+72-2a = 87 ; a = 87-72 = 15 ; b = 36-a = 36-15 = 21 ;
Fie ,,a " si ,,b " cele doua numere
3 × a + 2 × b = 87, iar a + b = 36
a + 2 × a + 2 × b = 87
a + 2 × ( a + b ) = 87
a + 2 × 36 = 87
a + 72 = 87
a = 87 - 72
a = 15
b = 36 - 15 ⇒ b = 21