1.
(3+x)×2=34+x
6+2x=34+x
x=34-6=28 ani
peste 28 de ani
2.
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abc7 =1000a+100b+10c+7
daca stergem 7
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abc =100a+10b+c
1000a+100b+10c+7-1816=100a+10b+c
900a+90b+9c=1809
100a+10b+c=201
c=1
b=0
a=2
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nr de forma abc7 este 2017
verificare daca stergem 7 devine 201 2017-201=1816