Răspuns:
X=vârsta tatălui
Y =vârsta fiului
9(Y-10)=X-10=9Y-90=X-10=9Y=X-10+90
=>9Y=X+80 |:9
Y=X+80/9
3(Y+2)=X+2
3(X+80/9+2) =X+2
X+80/3 +6=X+2
6-2=X-X+80/3
4=X-X+80/3 | x 3
12=3X-X-80
12=2X-80
12+80=2X
92=2X |:2=> X=46
Y=X+80/9 =46+80/9=126/9=14
......
V:9(14-10)=46-10
9 x 4=36
36=36(A)