Diana si Tudor au impreuna 610 lei, Tudor si Cosmin au impreuna 580 lei, iar Diana si Cosmin au impreuna 650 lei. Ce suma are fiecare copil?

Răspuns :

d+t=610
t+c=580=>t=580-c
d+c=650=>d=650-c

650-c+580-c=610
1230-2c=610
-2c=610-1230
-2c=-620/×(-1)
2c=620
c=620:2
c=310lei Cosmin

t+310=580
t=580-310
t=270lei Tudor

d+310=650
d=650-310
d=340lei Diana