a)x:10=c rest 3
x=10c+3
x-3=10c+3-3
x-3=10c
x-3∈M[10]
M10={1,10,20,30,40,50,60............}
x-3=10⇒x=10+3⇒x=13
13:10=1 rest 3 e bun
x-3=20⇒x=20+3⇒x=23
23:10=2 rest 3 e bun
.......................
nr. mai mici decat 60 sunt:13,23,33,43,53
2)
a+b=142
a;b=8 rest 7
a=8b+7
8b+7+b=142
9b=142-7
b=135/9
b=15
a=142-b=142-15
a=127
3)
3²⁵=(2+1)²⁵=2²⁵+1²⁵=2²⁵
deci 3²⁵<2³⁹