Răspuns:
11.
a+b=40 |×(-10)
10a+50b=1000
-10a-10b=(-400)
____________ +
/ 40b = 600 => b=15 bancnote de 50 lei => 25 bancnote de 10 lei
12.
a+b=135
a=2b/3
2b/3 + b = 135
2b+3b=135×3
5b=135×3
b=(135×3)/5
b=81 dm => a=54 dm