a= timbrele lui Marcel
b=timbrele lui Mugur
a+b=405 (*)
dar si b+15=3a
Adun numarul 15 in toata ecuatia notata (*) si obtin : a+(b+15)=420
dar mai stiu ca b+15=3a si inlocuiesc in ecuatia de mai sus, obtinand:
a+3a=420
4a=420
=>a=105 timbre
a+b=405=>b=405-a=405-105=300 => b=300timbre
Raspuns : Marcel are 105 timbre, iar Mugur are 300 de timbre.
