a+b+c=1124
b:a=3 si rest 459 b=3a+459
c:a=3 si rest 30 c=3a+30
a+3a+459+3a+30=1124
7a=1124-489
7a=635
a=635/7
b=3a+459=3×635/7+459=1905/7+459=5118/7
c=3a+30=3×635/7+30=1905/7+30=2115/7
verificare
a+b+c=635/7+5118/7+2115/7=7868/7=1124
2.a-b=665
a:b=6 si rest 50 a=6b+50
6b+50-b=665
5b=615
b=123
a=6*123+50=788
3.1×8+7=15
2×8+7=23
3×8+7=31
4×8+7=39
5×8+7=47
6×8+7=55
7×8+7=63
8×8+7=71
9×8+7=79
suma lor 15+23+31+39+47+55+63+71+79=8(1+2+...+9)+9*7=8*9*10/2+63=
=360+63=423