Răspuns :
x-nr total de banane
a+b+c=x
x-105=a
b=3a
b=3(x-105)=3x-315
c=a+b
c=x-105+3x-315
c=4x-420
x-105+3x-315+4x-420=x
8x-840=x
8x-x=840
7x=840
x=120
a=120-105
a=15
b=3*120-315=360-315
b=45
c=4*120-420=480-420
c=60
a+b+c=x
x-105=a
b=3a
b=3(x-105)=3x-315
c=a+b
c=x-105+3x-315
c=4x-420
x-105+3x-315+4x-420=x
8x-840=x
8x-x=840
7x=840
x=120
a=120-105
a=15
b=3*120-315=360-315
b=45
c=4*120-420=480-420
c=60
a+b+c=x
a+105=x ⇒ b+c=105 (3)
b=3a (1)
c=a+b=a+3a=4a (2)
(1) si (2) inlocuiesc in (3) ⇒ 3a+4a=105⇒ 7a=105⇒ a=105:7=15⇒b=3*15=45 ⇒ c=4*15=60
verificare 45+60= 105
a+105=x ⇒ b+c=105 (3)
b=3a (1)
c=a+b=a+3a=4a (2)
(1) si (2) inlocuiesc in (3) ⇒ 3a+4a=105⇒ 7a=105⇒ a=105:7=15⇒b=3*15=45 ⇒ c=4*15=60
verificare 45+60= 105