7(10a+b)-10b-a=
=70a+7b-10b-a=
=69a-3b=
=3(23a-b) deci divizibil cu 3
a+a+2+a+4=24
3a+6=24
3a=24-6
3a=18
a=6
numerele sunt 6,8 si 10
15=3x5
N+3=3 N=0
N+3=5
N=2
N+3=15
N=15-3=12
a0b+b0a multiplu de 101
100a+b+100b+a= 101a+101b=101 · (a+b) deci multiplu de 101
8,12,16,24,28,32,36,44,48,52,56,