Question

Daca 5 Kg de banana si 10kg de portocale costa 50 lei, iar 7 kg banana si 3 kg de portocale costa 37 lei, cat costa 1 kg din fiecare?

Answer 1

5b + 10 p = 50        | * 3   
7b + 3p = 37         | * 10

15b + 30p = 150
70b + 30p = 370
se scad
55b = 220
b = 220 : 55
b = 4 lei/kg banane
7 * 4 + 3p = 37
3p = 37 - 28
3p = 9
p = 9 : 3
p = 3 lei/kg portocale

Answer 2

5B+10P=50  
7B+3P=37
5B+10P=50   ⇒5B=50-10P⇒B=(50-10P):5
se introduce B in a 2 a ecuatie si rezulta\
7(50-10P):5)+3P=37 se aduce la acelasi numitor (5)
7(50-10P)+3*5*P=37*5
350-70P+15P=185    350-185=55P⇒  P=165:55⇒
P=3 lei kg de portocale

B=(50-10P):5
B=(50-10*3):5= 20:5=4 lei kg banane
B= 4 lei kg banane
Verificare:
7B+3P=37   7*4+3*3=28+9=37